Q.$\int_{0}^{\pi/2} \cos x\,e^{\sin x}\,dx =$ _______.

Showing the 12 most recent of 16 on this concept.

1. COMEDK 2026Set 2026-A1 markMCQ
   Q.

   [!FORMULA] $\int \frac{d x}{x \sqrt{x^2+4}}=$

   (A) $\frac{1}{4} \log \left|\frac{\sqrt{x^2+4}-2}{\sqrt{x^2+4}+2}\right|+C$ (B) $\frac{1}{4} \log \left|\frac{\sqrt{x^2+4}+2}{\sqrt{x^2+4}-2}\right|+C$ (C) $\frac{1}{2} \log \left|\frac{\sqrt{x^2+4}+2}{\sqrt{x^2+4}-2}\right|+C$ (D) $\frac{1}{2} \log \left|\frac{\sqrt{x^2+4}-2}{\sqrt{x^2+4}+2}\right|+C$

   ›Reveal solutionSolution

   Substituting $x=2\tan\theta$ gives $\frac{1}{4}\log\left|\frac{\sqrt{x^2+4}-2}{\sqrt{x^2+4}+2}\right|+C$ — option (A).

   For $\displaystyle\int\frac{dx}{x\sqrt{x^2+4}}$ put $x=2\tan\theta$, so $dx=2\sec^2\theta\,d\theta$ and $\sqrt{x^2+4}=2\sec\theta$:

   $\int\frac{2\sec^2\theta\,d\theta}{2\tan\theta\cdot 2\sec\theta}=\frac{1}{2}\int\csc\theta\,d\theta=\frac{1}{2}\log\left|\csc\theta-\cot\theta\right|+C$

   With $\csc\theta=\dfrac{\sqrt{x^2+4}}{x}$ and $\cot\theta=\dfrac{2}{x}$:

   $=\frac{1}{2}\log\left|\frac{\sqrt{x^2+4}-2}{x}\right|+C$ …

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2. COMEDK 2026Set 2026-M1 markMCQ
   Q.

   [!FORMULA] $\int \frac{x+1}{x\left(1+x e^x\right)} d x=$

   (A) $\log \left|c x e^x\left(1+x e^x\right)\right|$ (B) $\log \left|c x e^x\left(1+x e^x\right)\right|$ (C) $\log \left|\frac{c\left(1+x e^x\right)}{x e^x}\right|$ (D) $\log \left|\frac{c x e^x}{1+x e^x}\right|$

   ›Reveal solutionSolution

   The integral simplifies by noticing the derivative of $x e^x$ appears in the denominator; the result is $\log\left|\frac{c\,x e^x}{1+x e^x}\right|$, which matches option (D).

   ---

   The key insight is that the integrand contains $x e^x$ in the denominator, and the derivative of $x e^x$ is $e^x(1+x)$. That derivative is almost exactly the numerator $x+1$, except for a factor of $e^x$. This suggests a substitution or a clever split of the fraction to reveal a logarithmic derivative.

   ---

   1. Rewrite the integrand to expose the derivative of $x e^x$. Notice that

   $\frac{d}{dx}(x e^x) = e^x + x e^x = e^x(1+x).$

   Our numerator is $x+1$, so we can write:

   $\frac{x+1}{x(1+x e^x)} = \frac{e^x(x+1)}{e^x \cdot x(1+x e^x)} = \frac{e^x(1+x)}{x e^x (1+x e^x)}.$

   The numerator is now exactly the derivative of $x e^x$.

   2. Perform a substitution. Let $t = x e^x$. Then $dt = e^x(1+x)\,dx$. The integral becomes:

   $\int \frac{e^x(1+x)}{x e^x (1+x e^x)}\,dx = \int \frac{dt}{t(1+t)}.$

   3. Decompose the rational function. Use partial fractions:

   $\frac{1}{t(1+t)} = \frac{1}{t} - \frac{1}{1+t}.$

   So the integral is:

   $\int \left(\frac{1}{t} - \frac{1}{1+t}\right) dt = \log|t| - \log|1+t| + C = \log\left|\frac{t}{1+t}\right| + C.$

   4. Substitute back. Since $t = x e^x$, we have: $\int \frac{x+1}{x(1+x e^x)}\,dx = \log\left|\frac{x e^x}{1 + x e^x}\right| + C.$ …

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3. COMEDK 2026Set 2026-M1 markMCQ
   Q.

   [!FORMULA] $\int \frac{e^{\log \left(1+\frac{1}{x^2}\right)}}{x^2+\frac{1}{x^2}} d x=$

   (A) $\frac{1}{\sqrt{2}} \tan ^{-1}\left(\frac{x^2+1}{x \sqrt{2}}\right)+C$ (B) $\frac{1}{\sqrt{2}} \tan ^{-1}\left(\frac{x^2-1}{\sqrt{2} x}\right)+C$ (C) $-\frac{1}{\sqrt{2}} \tan ^{-1}\left(x-\frac{1}{x}\right)+C$ (D) $\frac{1}{\sqrt{2}} \tan ^{-1}\left(x-\frac{1}{x}\right)+C$

   ›Reveal solutionSolution

   The integrand simplifies dramatically using exponent rules and algebraic manipulation, leading to a standard arctangent integral; the correct antiderivative matches option (D).

   We start with the integral

   $\int \frac{e^{\log \left(1+\frac{1}{x^2}\right)}}{x^2+\frac{1}{x^2}} \, dx.$

   Concept & Intuition

   The presence of $e^{\log(\cdots)}$ is a huge clue: for any positive argument, $e^{\log(u)} = u$. That immediately collapses the numerator into something algebraic. Then the denominator is symmetric in $x$ and $1/x$, which often suggests a substitution like $t = x - 1/x$ because its derivative appears in the numerator. This is a classic trick for integrals involving $x^2 + 1/x^2$.

   ---

   Step-by-step solution

   1. Simplify the exponential Since $e^{\log(u)} = u$ for $u>0$ (and $1+1/x^2 > 0$ for all real $x \neq 0$), we have

   $e^{\log\left(1+\frac{1}{x^2}\right)} = 1 + \frac{1}{x^2}.$

   So the integral becomes

   $\int \frac{1 + \frac{1}{x^2}}{x^2 + \frac{1}{x^2}} \, dx.$

   2. Rewrite numerator and denominator Multiply numerator and denominator by $x^2$ to clear fractions:

   $\frac{1 + \frac{1}{x^2}}{x^2 + \frac{1}{x^2}} = \frac{x^2 + 1}{x^4 + 1}.$

   So the integral is

   $\int \frac{x^2 + 1}{x^4 + 1} \, dx.$

   3. Divide numerator and denominator by $x^2$ This is the key algebraic trick:

   $\frac{x^2 + 1}{x^4 + 1} = \frac{1 + \frac{1}{x^2}}{x^2 + \frac{1}{x^2}}.$

   Notice that the numerator $1 + 1/x^2$ is the derivative of $x - 1/x$ (since $\frac{d}{dx}(x - 1/x) = 1 + 1/x^2$).

   Also, $x^2 + 1/x^2 = (x - 1/x)^2 + 2$.

   4. Substitute Let $t = x - \frac{1}{x}$. Then

   $dt = \left(1 + \frac{1}{x^2}\right) dx.$

   And

   $x^2 + \frac{1}{x^2} = t^2 + 2.$

   The integral becomes

   $\int \frac{dt}{t^2 + 2}.$

   5. Integrate This is a standard arctangent form:

   $\int \frac{dt}{t^2 + a^2} = \frac{1}{a} \tan^{-1}\left(\frac{t}{a}\right) + C.$

   Here $a = \sqrt{2}$, so

   $\int \frac{dt}{t^2 + 2} = \frac{1}{\sqrt{2}} \tan^{-1}\left(\frac{t}{\sqrt{2}}\right) + C.$

   6. Back-substitute Replace $t$ with $x - \frac{1}{x}$:

   $\frac{1}{\sqrt{2}} \tan^{-1}\left(\frac{x - \frac{1}{x}}{\sqrt{2}}\right) + C.$

   Simplify the argument:

   $\frac{x - \frac{1}{x}}{\sqrt{2}} = \frac{x^2 - 1}{\sqrt{2}\, x}.$

   So the antiderivative is

   $\frac{1}{\sqrt{2}} \tan^{-1}\left(\frac{x^2 - 1}{\sqrt{2}\, x}\right) + C.$ …

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4. KCET 2026Set UNKNOWN1 markMCQ
   Q.If 'n' is a natural number, then $\int \frac{\sin^n x}{\cos^{n+2} x}dx =$ (A) $\frac{\tan^{n-1}x}{n-1} + C$ (B) $\frac{\tan^n x}{n} + C$ (C) $\frac{\tan^{n+2}x}{n+2} + C$ (D) $\frac{\tan^{n+1}x}{n+1} + C$

   ›Reveal solutionSolution

   Split the integrand into $\tan^n x$ and $\sec^2 x$, then substitute $t=\tan x$.

   Step 1 — Rewrite the integrand

   $\frac{\sin^n x}{\cos^{n+2} x} = \frac{\sin^n x}{\cos^n x}\cdot\frac{1}{\cos^2 x} = \tan^n x \sec^2 x$

   Step 2 — Substitute

   Let $t = \tan x$, so $dt = \sec^2 x\,dx$: …

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5. COMEDK 2025Set 2025-A1 markMCQ
   Q.$\int \frac{e^{\tan ^{-1} x}}{\left(1+x^2\right)}\left(1+x+x^2\right) d x=$ (A) $e^{\tan ^{-1} x}+c$ (B) $x e^{\tan ^{-1} x}+c$ (C) $\frac{e^{\tan ^{-1} x}}{\left(1+x^2\right)}+c$ (D) $\frac{x e^{\tan ^{-1} x}}{\left(1+x^2\right)}+c$

   ›Reveal solutionSolution

   The integral simplifies by substituting $u = \tan^{-1} x$, which turns the expression into a sum of a standard exponential integral and a derivative-of-product pattern, yielding $x e^{\tan^{-1} x} + C$. The correct option is (B).

   ---

   The key insight is that the denominator $1+x^2$ is exactly the derivative of $\tan^{-1} x$, so the substitution $u = \tan^{-1} x$ is natural. Once we do that, the polynomial $1+x+x^2$ becomes something in terms of $\tan u$, and we can split the integral into two recognizable pieces.

   1. Substitute $u = \tan^{-1} x$. Then $du = \frac{dx}{1+x^2}$, and $x = \tan u$. The integral becomes

   $\int e^{\tan^{-1} x} \cdot \frac{1+x+x^2}{1+x^2}\,dx = \int e^{u} \left(1 + \tan u + \tan^2 u\right) du.$

   2. Simplify the trigonometric expression. Recall $1 + \tan^2 u = \sec^2 u$. So

   $1 + \tan u + \tan^2 u = \sec^2 u + \tan u.$

   The integral is now

   $\int e^{u} (\sec^2 u + \tan u)\, du.$

   3. Split and recognize patterns.

   $\int e^{u} \sec^2 u \, du + \int e^{u} \tan u \, du.$

   Notice that $\frac{d}{du}(\tan u) = \sec^2 u$. The first integral is of the form $\int e^{u} f'(u) du$ with $f(u) = \tan u$, and the second is $\int e^{u} f(u) du$.

   4. Use the product rule in reverse. For any differentiable $f(u)$,

   $\frac{d}{du}\left( e^{u} f(u) \right) = e^{u} f'(u) + e^{u} f(u).$

   Here $f(u) = \tan u$, so

   $$$$

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6. COMEDK 2024Set 2024-A1 markMCQ
   Q.

   [!FORMULA] $\int \frac{f^{\prime}(x)}{f(x) \log (f(x))} d x \text { is equal to }$

   (A) $f(x) \log f(x)+C$ (B) $\frac{1}{\log (\log f(x))}+C$ (C) $\frac{f(x)}{\log f(x)}+C$ (D) $\log (\log f(x))+C$

   ›Reveal solutionSolution

   The integral simplifies by substitution $u = \log(f(x))$, leading directly to $\log(\log f(x)) + C$, so the correct choice is (D).

   Concept & Intuition

   When you see a fraction where the numerator is the derivative of the denominator’s “inside,” a substitution is almost always the cleanest path. Here, the denominator is $f(x) \log(f(x))$, and the numerator is $f'(x)$. Notice that the derivative of $\log(f(x))$ is $\frac{f'(x)}{f(x)}$, which appears in the integrand. That suggests setting $u = \log(f(x))$, turning the whole integral into a simple $\int \frac{du}{u}$.

   Step-by-step solution

   1. Identify the substitution Let $u = \log(f(x))$. Then differentiate:

   $\frac{du}{dx} = \frac{f'(x)}{f(x)} \quad\Rightarrow\quad du = \frac{f'(x)}{f(x)}\,dx.$

   2. Rewrite the integral The original integral is

   $\int \frac{f'(x)}{f(x) \log(f(x))}\,dx.$

   Factor the $f(x)$ in the denominator:

   $\int \frac{f'(x)/f(x)}{\log(f(x))}\,dx.$

   Now substitute $u = \log(f(x))$ and $du = \frac{f'(x)}{f(x)}dx$:

   $\int \frac{du}{u}.$

   3. Integrate The integral $\int \frac{du}{u}$ is a standard result:

   $\int \frac{du}{u} = \log|u| + C.$

   4. Back-substitute Replace $u$ with $\log(f(x))$: $\log|\log(f(x))| + C.$ …

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7. COMEDK 2024Set 2024-M1 markMCQ
   Q.If $\int \frac{1}{\sqrt{\sin ^3 x \cos x}} d x=\frac{k}{\sqrt{\tan x}}+c$ then the value of $k$ is (A) $-2$ (B) 1 (C) 2 (D) $-1$

   ›Reveal solutionSolution

   The integral simplifies by rewriting the integrand in terms of $\tan x$, leading to a straightforward power rule integration; comparing the result with the given form shows $k = -2$.

   We are given

   $\int \frac{1}{\sqrt{\sin^3 x \cos x}}\, dx = \frac{k}{\sqrt{\tan x}} + c$

   and need to find $k$.

   Concept and intuition

   The integrand mixes powers of $\sin x$ and $\cos x$. A classic trick is to express everything in terms of $\tan x$ (or $\cot x$) because the derivative of $\tan x$ is $\sec^2 x$, which itself is $1/\cos^2 x$. This often turns messy trigonometric integrals into simple power rules. Here, the presence of $\sqrt{\tan x}$ on the right side is a strong hint: the integrand likely simplifies to something like $(\tan x)^{-3/2} \cdot \sec^2 x$, whose antiderivative is a constant times $(\tan x)^{-1/2}$.

   Let’s work it out step by step.

   1. Rewrite the integrand using $\tan x$.

   $\frac{1}{\sqrt{\sin^3 x \cos x}} = \frac{1}{\sin^{3/2} x \cdot \cos^{1/2} x}$

   Divide numerator and denominator by $\cos^{3/2} x$ (a common trick to introduce $\tan x$):

   $= \frac{1}{\cos^{3/2} x \cdot \tan^{3/2} x \cdot \cos^{1/2} x} = \frac{1}{\cos^{2} x \cdot \tan^{3/2} x}$

   because $\cos^{3/2} x \cdot \cos^{1/2} x = \cos^2 x$.

   Since $1/\cos^2 x = \sec^2 x$, we have:

   $\frac{1}{\sqrt{\sin^3 x \cos x}} = \frac{\sec^2 x}{\tan^{3/2} x}.$

   2. Set up the substitution. Let $u = \tan x$. Then $du = \sec^2 x \, dx$. The integral becomes:

   $\int \frac{\sec^2 x}{\tan^{3/2} x}\, dx = \int \frac{du}{u^{3/2}} = \int u^{-3/2}\, du.$

   3. Integrate using the power rule. $\int u^{-3/2}\, du = \frac{u^{-3/2+1}}{-3/2+1} = \frac{u^{-1/2}}{-1/2} = -2\, u^{-1/2} + C.$ …

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8. COMEDK 2024Set 2024-M1 markMCQ
   Q.

   [!FORMULA] $\text { The value of } \int \frac{1}{x+\sqrt{x-1}} d x \text { is }$

   (A) $\log (x+\sqrt{x-1})+\sin ^{-1}\left(\sqrt{\frac{x-1}{x}}\right)+C$ (B) $\log (x+\sqrt{x-1})-\frac{2}{\sqrt{3}} \tan ^{-1}\left(\frac{2 \sqrt{x-1}+1}{\sqrt{3}}\right)+C$ (C) $\log (x+\sqrt{x-1})+C$ (D) $\log (x-1+\sqrt{x-1})+\frac{1}{\sqrt{3}} \log \left|\frac{x-2-\sqrt{3}}{x-2+\sqrt{3}}\right|+C$

   ›Reveal solutionSolution

   The integral simplifies by substituting $t = \sqrt{x-1}$, turning it into a rational function that integrates to a logarithm and an arctangent, matching option (B).

   We are asked to evaluate

   $\int \frac{1}{x + \sqrt{x-1}} \, dx.$

   The presence of $\sqrt{x-1}$ suggests a substitution that removes the square root, turning the integrand into a rational function. The trick is to set $t = \sqrt{x-1}$, so that $x = t^2 + 1$ and $dx = 2t \, dt$. This transforms the integral into a form we can handle with partial fractions or a standard arctangent formula.

   Let’s work through it step by step.

   1. Substitute $t = \sqrt{x-1}$. Then $x = t^2 + 1$ and $dx = 2t \, dt$. The denominator becomes

   $x + \sqrt{x-1} = (t^2 + 1) + t = t^2 + t + 1.$

   So the integral becomes

   $\int \frac{1}{t^2 + t + 1} \cdot 2t \, dt = 2 \int \frac{t}{t^2 + t + 1} \, dt.$

   2. Prepare for integration by rewriting the numerator to match the derivative of the denominator. The derivative of $t^2 + t + 1$ is $2t + 1$. We have $2t$ in the numerator, so write

   $2t = (2t + 1) - 1.$

   Then

   $2 \int \frac{t}{t^2 + t + 1} \, dt = \int \frac{2t + 1}{t^2 + t + 1} \, dt - \int \frac{1}{t^2 + t + 1} \, dt.$

   3. First integral:

   $\int \frac{2t + 1}{t^2 + t + 1} \, dt = \log|t^2 + t + 1| + C_1.$

   Since $t^2 + t + 1 > 0$ for all real $t$, we can drop the absolute value.

   4. Second integral: Complete the square in the denominator:

   $t^2 + t + 1 = \left(t + \frac12\right)^2 + \frac34.$

   So

   $\int \frac{1}{t^2 + t + 1} \, dt = \int \frac{1}{\left(t + \frac12\right)^2 + \left(\frac{\sqrt{3}}{2}\right)^2} \, dt.$

   Using the formula $\int \frac{du}{u^2 + a^2} = \frac{1}{a} \tan^{-1}\left(\frac{u}{a}\right)$, with $u = t + \frac12$ and $a = \frac{\sqrt{3}}{2}$, we get

   $\int \frac{1}{t^2 + t + 1} \, dt = \frac{2}{\sqrt{3}} \tan^{-1}\left( \frac{2t + 1}{\sqrt{3}} \right) + C_2.$

   5. Combine results: $$$$

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9. KCET 2023Set A-21 markMCQ
   Q.If $u = \sin^{-1}\left(\dfrac{2x}{1+x^2}\right)$ and $v = \tan^{-1}\left(\dfrac{2x}{1-x^2}\right)$ then $\dfrac{du}{dv}$ is (A) $2$ (B) $\dfrac{1-x^2}{1+x^2}$ (C) $1$ (D) $\dfrac{1}{2}$

   ›Reveal solutionSolution

   The key idea is to simplify $u$ and $v$ using standard inverse trigonometric identities before differentiating. The result is $\frac{du}{dv} = 1$.

   We are given two functions of $x$:

   $u = \sin^{-1}\left(\frac{2x}{1+x^2}\right), \quad v = \tan^{-1}\left(\frac{2x}{1-x^2}\right).$

   The question asks for $\frac{du}{dv}$, the derivative of $u$ with respect to $v$. A direct approach — differentiating each with respect to $x$ and then dividing — is possible, but messy. A cleaner path is to recognize that both expressions are standard forms for inverse trigonometric functions when $x = \tan \theta$.

   1. Substitute $x = \tan \theta$. This is a classic trick because $\frac{2x}{1+x^2}$ and $\frac{2x}{1-x^2}$ appear in double-angle formulas. Let $\theta = \tan^{-1} x$, so $x = \tan \theta$. Then:

   $\frac{2x}{1+x^2} = \frac{2\tan\theta}{1+\tan^2\theta} = \sin 2\theta.$

   Hence,

   $u = \sin^{-1}(\sin 2\theta).$

   2. Simplify $u$ carefully. The identity $\sin^{-1}(\sin \alpha) = \alpha$ holds only when $\alpha$ is in the principal range $[-\pi/2, \pi/2]$. Here $\alpha = 2\theta$, and $\theta = \tan^{-1} x$ lies in $(-\pi/2, \pi/2)$. So $2\theta$ lies in $(-\pi, \pi)$. For $u$ to be defined as the principal value of $\sin^{-1}$, we need $2\theta \in [-\pi/2, \pi/2]$, which corresponds to $x \in [-1, 1]$. In that interval, we can safely write:

   $u = 2\theta = 2\tan^{-1} x.$

   Watch out

   Outside $x \in [-1, 1]$, the simplification $u = 2\tan^{-1} x$ would be off by a constant (like $\pi - 2\tan^{-1} x$). However, the derivative $\frac{du}{dx}$ remains the same because the constant vanishes. So the derivative result holds for all $x$ where the functions are defined.

   3. Simplify $v$ similarly. Using $x = \tan \theta$ again:

   $\frac{2x}{1-x^2} = \frac{2\tan\theta}{1-\tan^2\theta} = \tan 2\theta.$

   Therefore,

   $v = \tan^{-1}(\tan 2\theta).$ …

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10. COMEDK 2023Set 2023-M1 markMCQ
    Q.$\int \frac{x d x}{2(1+x)^{3 / 2}}$ is equal to (A) $\frac{2+x}{\sqrt{1+x}}+C$ (B) $\frac{2+x}{x \sqrt{1+x}}+C$ (C) $\frac{x}{\sqrt{1+x}}+C$ (D) $-\frac{x}{\sqrt{1+x}}+C$

    ›Reveal solutionSolution

    With $u=1+x$, the integral becomes $\tfrac12\int(u^{-1/2}-u^{-3/2})\,du=u^{1/2}+u^{-1/2}=\dfrac{2+x}{\sqrt{1+x}}+C$.

    $\displaystyle\int\frac{x\,dx}{2(1+x)^{3/2}}.$ Let $u=1+x\Rightarrow x=u-1,\ dx=du$:

    $\frac12\int\frac{u-1}{u^{3/2}}\,du=\frac12\int\left(u^{-1/2}-u^{-3/2}\right)du.$ …

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11. COMEDK 2023Set 2023-M1 markMCQ
    Q.$\int \frac{4^x}{\sqrt{1-16^x}} d x$ is equal to (A) $(\log 4) \sin ^{-1} 4^x+C$ (B) $\frac{1}{4} \sin ^{-1}\left(4^x\right)+C$ (C) $\frac{1}{\log 4} \sin ^{-1} 4^x+C$ (D) $4 \log 4 \sin ^{-1} 4+C$

    ›Reveal solutionSolution

    Put $u=4^x$ so $16^x=u^2$ and $du=4^x\ln4\,dx$; the integral becomes $\dfrac{1}{\ln4}\int\dfrac{du}{\sqrt{1-u^2}}=\dfrac{1}{\log4}\sin^{-1}(4^x)+C$.

    $\displaystyle\int\frac{4^x}{\sqrt{1-16^x}}\,dx.$ Let $u=4^x\Rightarrow du=4^x\ln4\,dx\Rightarrow 4^x\,dx=\dfrac{du}{\ln4}$, and $16^x=(4^x)^2=u^2$: …

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12. COMEDK 2022Set 20221 markMCQ
    Q.$\int \frac{3^x}{\sqrt{1-9^x}} d x$ is equal to (A) $(\log 3) \sin ^{-1} 3^x+C$ (B) $\frac{1}{3} \sin ^{-1}\left(3^x\right)+C$ (C) $\frac{1}{\log 3} \sin ^{-1} 3^x+C$ (D) $3 \log 3 \sin ^{-1} 3^x+C$

    ›Reveal solutionSolution

    I = (1/log 3) * Integral du / sqrt(1 - u^2) = (1/log 3) * arcsin(u) + C = (1 / log 3) * sin^-1 (3^x) + C

    Concept: Substitution reducing to the arcsin form, integral du/sqrt(1 - u^2) = arcsin u.

    I = Integral of 3^x / sqrt(1 - 9^x) dx , and 9^x = (3^x)^2

    Put u = 3^x => du = 3^x (log 3) dx => 3^x dx = du / log 3

    I = (1/log 3) * Integral du / sqrt(1 - u^2) …

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