Q.Integrate the following function: $\cos 3x$

Showing the 12 most recent of 44 on this concept.

1. CBSE 2026Set 65/1/11 markMCQ
   Q.If $\int \frac{3ax}{b^2 + c^2x^2} dx = A \log |b^2 + c^2x^2| + K$, then the value of A is: (A) $3a$ (B) $\frac{3a}{2b^2}$ (C) $\frac{3a}{b^2c^2}$ (D) $\frac{3a}{2c^2}$

   ›Reveal solutionSolution

   The integral fits the pattern $\int \frac{du}{u} = \log|u| + C$ after a substitution. The constant $A$ turns out to be $\frac{3a}{2c^2}$, which corresponds to option (D).

   The problem gives you the result of an integral and asks you to identify the constant $A$ that makes the equation true. This is a classic "match the form" question — you don't need to guess; you just need to perform the integration carefully and compare.

   The key insight is that the integrand $\frac{3ax}{b^2 + c^2x^2}$ is a rational function where the numerator is almost the derivative of the denominator. The derivative of $b^2 + c^2x^2$ is $2c^2x$. Our numerator is $3ax$, which is a constant multiple of $x$. So a simple substitution $u = b^2 + c^2x^2$ will turn the integral into $\int \frac{du}{u}$.

   Let's work through it step by step.

   1. Set up the substitution.

      Let $u = b^2 + c^2x^2$. Then $du = 2c^2x \, dx$, so $x \, dx = \frac{du}{2c^2}$.

   2. Rewrite the integral in terms of $u$.

      The integral is $\int \frac{3ax}{b^2 + c^2x^2} \, dx = \int \frac{3a}{u} \cdot (x \, dx)$.

      Substitute $x \, dx = \frac{du}{2c^2}$:

   $\int \frac{3a}{u} \cdot \frac{du}{2c^2} = \frac{3a}{2c^2} \int \frac{du}{u}.$

   3. Integrate. $\int \frac{du}{u} = \log|u| + C$, so

   $\frac{3a}{2c^2} \log|u| + C = \frac{3a}{2c^2} \log|b^2 + c^2x^2| + K,$

   where $K$ is the constant of integration (we renamed $C$ to $K$ to match the problem).

   4. Compare with the given form. The problem states that the integral equals $A \log|b^2 + c^2x^2| + K$. Matching coefficients, we see

   $A = \frac{3a}{2c^2}.$

   Watch out

   A common mistake is to forget the factor from $du$ — specifically, that $x\,dx$ becomes $\frac{du}{2c^2}$, not just $du$. If you skip that, you might get $3a$ or something like $\frac{3a}{2b^2}$, which are wrong. Always check the derivative of your substitution.

   Tip

   Notice that the constants $b^2$ and $c^2$ appear in the denominator, but $b^2$ disappears from the final $A$ because it's part of the constant term inside the log — it doesn't affect the coefficient. Only $c^2$ matters because it comes from the derivative.

   ✓Final answer

   The value of $A$ is $\boxed{\frac{3a}{2c^2}}$, which corresponds to option (D).

2. CBSE 2026Set CX1 mark
   Q.Find the value of the integral $\int x^{2}\tan(x^{3}+2)\,dx$.

   ›Reveal solutionSolution

   Substitute $u=x^{3}+2$; the integral becomes $\tfrac13\int\tan u\,du=\tfrac13\ln|\sec(x^{3}+2)|+C$.

   Concept: The factor $x^{2}$ is (up to a constant) the derivative of the inner function $x^{3}+2$, so substitution works.

   Let $u=x^{3}+2\Rightarrow du=3x^{2}\,dx\Rightarrow x^{2}\,dx=\dfrac{du}{3}$.

   $\int x^{2}\tan(x^{3}+2)\,dx=\dfrac13\int\tan u\,du=\dfrac13\ln|\sec u|+C.$

   Replacing $u$:

   $=\dfrac13\ln\big|\sec(x^{3}+2)\big|+C.$

   ✓Final answer

   $\displaystyle\int x^{2}\tan(x^{3}+2)\,dx=\dfrac{1}{3}\ln\big|\sec(x^{3}+2)\big|+C.$

3. CBSE 2026Set A1 markMCQ
   Q.$\int\frac{\tan(\sin^{-1}x)}{\sqrt{1-x^2}}\,dx =$

   (a) $\log|\sec(\sin^{-1}x)| + k$

   (b) $\log|\cos(\sin^{-1}x)| + k$

   (c) $\tan(\sin^{-1}x) + k$

   (d) $\log|\sin^{-1}x| + k$

   ›Reveal solutionSolution

   With $u=\sin^{-1}x$ (so $du=\tfrac{dx}{\sqrt{1-x^2}}$) the integral is $\int\tan u\,du=\log|\sec u|+k$.

   Let $u=\sin^{-1}x$. Then $du=\dfrac{dx}{\sqrt{1-x^2}}$, so

   $\int\dfrac{\tan(\sin^{-1}x)}{\sqrt{1-x^2}}\,dx=\int\tan u\,du=\log|\sec u|+k=\log|\sec(\sin^{-1}x)|+k$.

   ✓Final answer

   (A) $\log|\sec(\sin^{-1}x)|+k$.

4. CBSE 2026Set A1 markMCQ
   Q.$\int\frac{dx}{e^x + e^{-x}} =$

   (a) $\cot^{-1}(e^x) + k$

   (b) $\tan^{-1}(e^x) + k$

   (c) $\log|e^x + 1| + k$

   (d) $\sin^{-1}(e^x) + k$

   ›Reveal solutionSolution

   Substitute $t=e^x$: $\int\tfrac{dx}{e^x+e^{-x}}=\int\tfrac{dt}{1+t^2}=\tan^{-1}(e^x)+k$.

   Multiply numerator and denominator by $e^x$:

   $\dfrac{1}{e^x+e^{-x}}=\dfrac{e^x}{e^{2x}+1}$.

   Let $t=e^x$, $dt=e^x\,dx$. Then

   $\int\dfrac{e^x\,dx}{e^{2x}+1}=\int\dfrac{dt}{t^2+1}=\tan^{-1}t+k=\tan^{-1}(e^x)+k$.

   ✓Final answer

   (B) $\tan^{-1}(e^x)+k$.

5. CBSE 2026Set ANNUAL1 markMCQ
   Q.$\int \sin(2x+3)\,dx =$

   (a) $\cos(2x+3)+C$

   (b) $-\dfrac{\cos(2x+3)}{2}+C$

   (c) $\tan 2x + C$

   (d) None of these

   ›Reveal solutionSolution

   $\int \sin(ax+b)\,dx = -\dfrac{\cos(ax+b)}{a}+C$.

   With $a=2, b=3$: $\int \sin(2x+3)\,dx = -\dfrac{\cos(2x+3)}{2}+C$.

   ✓Final answer

   (b) $-\dfrac{\cos(2x+3)}{2}+C$.

6. CBSE 2026Set ANNUAL1 markMCQ
   Q.$\displaystyle\int_1^{e} \dfrac{(\log x)^2}{x}\, dx =$

   (a) $\dfrac{1}{3}e^3$

   (b) $\dfrac{1}{3}(e^3-1)$

   (c) $\dfrac{1}{3}$

   (d) None of these

   ›Reveal solutionSolution

   Substitute $u = \log x$, $du = dx/x$, converting the limits from $x=1,e$ to $u=0,1$.

   Let $u=\log x \Rightarrow du = \dfrac{dx}{x}$. When $x=1, u=0$; when $x=e, u=1$.

   $\displaystyle\int_1^e \dfrac{(\log x)^2}{x}dx = \int_0^1 u^2\,du = \left[\dfrac{u^3}{3}\right]_0^1 = \dfrac{1}{3}$.

   ✓Final answer

   (c) $\dfrac{1}{3}$.

7. CBSE 2026Set ANNUAL1 markMCQ
   Q.$\displaystyle\int \dfrac{1}{x(1+\log x)}\,dx$ is equal to:

   (a) $x + \log x + c$

   (b) $|x + \log x| + c$

   (c) $\log|1 + \log x| + c$

   (d) $\log(1+x) + c$

   ›Reveal solutionSolution

   Substitute $u=1+\log x$ so $du=\dfrac{dx}{x}$, turning the integral into $\int\dfrac{du}{u}$.

   $I=\displaystyle\int\dfrac{1}{x(1+\log x)}\,dx$

   Let $u=1+\log x \Rightarrow du=\dfrac{1}{x}dx$.

   $I=\displaystyle\int\dfrac{du}{u}=\log|u|+c=\log|1+\log x|+c$

   ✓Final answer

   Option (c): $\log|1+\log x|+c$

8. CBSE 2026Set ANNUAL1 markMCQ
   Q.$\displaystyle\int \dfrac{\sin^6 x}{\cos^8 x}\,dx$ is equal to:

   ›Reveal solutionSolution

   Rewrite the integrand as $\tan^6x\sec^2x$ and substitute $t=\tan x$.

   $I=\displaystyle\int\dfrac{\sin^6x}{\cos^8x}\,dx=\int\dfrac{\sin^6x}{\cos^6x}\cdot\dfrac{1}{\cos^2x}\,dx=\int\tan^6x\sec^2x\,dx$

   Let $t=\tan x \Rightarrow dt=\sec^2x\,dx$.

   $I=\displaystyle\int t^6\,dt=\dfrac{t^7}{7}+c=\dfrac{\tan^7x}{7}+c$

   ✓Final answer

   $\dfrac{\tan^7 x}{7}+c$

9. CBSE 2026Set ANNUAL1 markMCQ
   Q.\int x^2 e^{x^3} dx equals:

   (a)

   (i) \frac{e^{x^3}}{3} + c

   (b)

   (ii) 3e^{x^3} + c

   (c)

   (iii) \frac{e^{x^2}}{3} + c

   (d)

   (iv) \frac{1}{2}e^{x^2} + c

   ›Reveal solutionSolution

   $\displaystyle\int x^2 e^{x^3}\,dx=\dfrac{e^{x^3}}{3}+c$ — option (i).

   Concept. Substitution ($u$-substitution): choose $u$ whose derivative already appears (up to a constant) in the integrand.

   Steps.

   • Let $u=x^3$, then $du=3x^2\,dx$, i.e. $x^2\,dx=\dfrac{1}{3}\,du$.

   • $\displaystyle\int x^2 e^{x^3}\,dx=\int e^{u}\cdot\dfrac{1}{3}\,du=\dfrac{1}{3}e^{u}+c$.

   • Back-substitute $u=x^3$: $\dfrac{e^{x^3}}{3}+c$.

   ✓Final answer

   $\dfrac{e^{x^3}}{3}+c$ — option (i).

10. CBSE 2025Set ANNUAL1 markMCQ
    Q.$\displaystyle\int \dfrac{\cos x}{1+\sin^2 x}\, dx =$

    (a) $-\tan^{-1}(\sin x) + c$

    (b) $\tan^{-1}(\cos x) + c$

    (c) $\tan^{-1}(\sin x) + c$

    (d) $-\tan^{-1}(\cos x) + c$

    ›Reveal solutionSolution

    A direct substitution u = sin x reduces this to the standard ∫du/(1+u²) form.

    Let $u=\sin x$, so $du = \cos x\,dx$.

    $\displaystyle\int \dfrac{\cos x}{1+\sin^2x}\,dx = \int\dfrac{du}{1+u^2} = \tan^{-1}u + c = \tan^{-1}(\sin x)+c$

    ✓Final answer

    (c) $\tan^{-1}(\sin x)+c$.

11. CBSE 2025Set ANNUAL1 mark
    Q.Evaluate ∫ 2x sin(1 - x^2) dx.

    ›Reveal solutionSolution

    Substitute $u = 1-x^2$ so $du = -2x\,dx$, turning the integral into a simple $\int \sin u\,du$.

    Let $u = 1 - x^2$. Then $\dfrac{du}{dx} = -2x \Rightarrow 2x\,dx = -du$.

    $\int 2x\sin(1-x^2)\,dx = \int \sin u \,(-du) = -\int \sin u\,du = -(-\cos u) + C = \cos u + C$

    Substituting back $u = 1-x^2$:

    ✓Final answer

    $\int 2x\sin(1-x^2)\,dx = \cos(1-x^2) + C$.

12. CBSE 2025Set ANNUAL1 mark
    Q.Evaluate: $\displaystyle\int_{2}^{\sqrt3} \dfrac{x\,dx}{x^2+1}$

    ›Reveal solutionSolution

    Substitute $u=x^2+1$ so the integrand becomes $\frac12\int\frac{du}{u}$, then apply the given limits (2 to $\sqrt3$) directly.

    $\int_{2}^{\sqrt3}\dfrac{x\,dx}{x^2+1}$

    Let $u = x^2+1$, so $du = 2x\,dx$, i.e. $x\,dx = \dfrac{du}{2}$.

    $\int\dfrac{x\,dx}{x^2+1} = \dfrac12\int\dfrac{du}{u} = \dfrac12\ln|u| = \dfrac12\ln(x^2+1)$

    Applying the limits exactly as given (lower limit $x=2$, upper limit $x=\sqrt3$):

    $\left[\dfrac12\ln(x^2+1)\right]_{2}^{\sqrt3} = \dfrac12\ln(3+1) - \dfrac12\ln(4+1) = \dfrac12\ln4 - \dfrac12\ln5 = \dfrac12\ln\dfrac{4}{5}$

    Since $4/5<1$, this value is negative (the integral runs from the larger limit $x=2$ down to the smaller limit $x=\sqrt3\approx1.73$, which reverses the usual sign):

    $\dfrac12\ln\dfrac45 = -\dfrac12\ln\dfrac54 \approx -0.1116$

    ✓Final answer

    $\displaystyle\int_{2}^{\sqrt3}\dfrac{x\,dx}{x^2+1} = \dfrac12\ln\dfrac{4}{5} = -\dfrac12\ln\dfrac{5}{4}$