Q.Integrate the function x2+4x+105x+3
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🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — U Substitution
U Substitution: The Reverse Chain Rule
The chain rule differentiates composite functions: the derivative of sin(x2) is cos(x2)⋅2x — differentiate the outer function, then multiply by the derivative of the inside. Integration asks the reverse: given cos(x2)⋅2x, find the original function. That's what u substitution does — it reverses the chain rule.
The Core Intuition
When an integral looks like "a function times the derivative of its inside," substitute the inside with u and the derivative of the inside with du. Consider:
∫2xcos(x2)dx
Here 2x is the derivative of x2, and x2 is the inside of cos(x2). Let u=x2, so du=2xdx:
∫cos(u)du=sin(u)+C=sin(x2)+C
Check: the derivative of sin(x2) is cos(x2)⋅2x.
The Precise Statement
∫f(g(x))⋅g′(x)dx=∫f(u)duwhere u=g(x),du=g′(x)dx
Valid provided g is differentiable and the resulting integral in u is simpler.
The Step-by-Step Method
- Identify a function g(x) whose derivative g′(x) also appears (possibly up to a constant factor).
- Set u=g(x), compute du=g′(x)dx.
- Rewrite the entire integral in u and du — every x and dx must be replaced.
- Integrate with respect to u.
- Substitute back u=g(x).
You cannot mix variables. If any x remains after substitution, you chose the wrong u (or must solve for x in terms of u — rare).
A Second Example (with a constant factor)
Evaluate ∫xx2+1dx. Let u=x2+1, so xdx=21du:
∫u⋅21du=21⋅32u3/2+C=31(x2+1)3/2+C
When Does It Work?
When the integrand is something times the derivative of something inside. Common patterns:
- x⋅f(x2) — derivative of x2 is 2x, so u=x2
- eg(x)⋅g′(x) — derivative of g(x) appears
- g(x)g′(x) — leads to log∣g(x)∣ …
Concept: U Substitution — we rewrite the numerator as a derivative of the denominator’s inside, then split into two standard integrals.
Step 1: Complete the square in the denominator:
x2+4x+10=(x+2)2+6.
So the integral becomes ∫(x+2)2+65x+3dx.
Step 2: Let u=x+2, so x=u−2, dx=du, and 5x+3=5(u−2)+3=5u−7.
The integral is now ∫u2+65u−7du.
Step 3: Split:
5∫u2+6udu−7∫u2+61du.
First integral: substitute t=u2+6, dt=2udu → 5⋅u2+6. …
The key idea is to rewrite the numerator as a derivative of the denominator’s radicand plus a constant, then split the integral into two simpler ones. The final result is 5x2+4x+10−7logx+2+x2+4x+10+C.
Why U-Substitution Works Here
When you see a square root of a quadratic in the denominator, your first instinct should be: can I make the numerator match the derivative of the expression inside the square root? That’s because the derivative of u is 2u1⋅u′, so if the numerator contains u′, the integral collapses into a simple power rule.
Here, the radicand is x2+4x+10. Its derivative is 2x+4. Our numerator is 5x+3, which is not exactly 2x+4, but we can force it to be a linear combination: 5x+3=A(2x+4)+B. Solve for A and B, and the integral splits into two parts — one a pure u-substitution, the other a standard inverse hyperbolic (or log) form.
-
Set up the split.
We want 5x+3=A(2x+4)+B.
Expand: 5x+3=2Ax+4A+B.
Compare coefficients:
- For x: 2A=5⟹A=25
- For constant: 4A+B=3⟹4⋅25+B=3⟹10+B=3⟹B=−7
So the integral becomes:
∫x2+4x+1025(2x+4)−7dx=25∫x2+4x+102x+4dx−7∫x2+4x+101dx
- First integral: pure u-substitution. Let u=x2+4x+10. Then du=(2x+4)dx. The first integral becomes:
25∫udu=25⋅2u+C1=5x2+4x+10+C1
- Second integral: complete the square. The denominator’s radicand: x2+4x+10=(x2+4x+4)+6=(x+2)2+6. So we need:
∫(x+2)2+61dx
This is a standard form: ∫t2+a21dt=logt+t2+a2+C, where a2=6 and t=x+2. …
Method: Linear numerator over the square root of a quadratic
Use this whenever the integrand is ax2+bx+cpx+q — a linear top over the root of a quadratic. The idea is to peel off the part of the numerator that is the derivative of the radicand, leaving a pure "1/quadratic" piece.
Steps
Step 1: Split the numerator against the radicand's derivative.
Write px+q=λdxd(ax2+bx+c)+μ=λ(2ax+b)+μ, and match the coefficient of x and the constant to solve for λ and μ.
Step 2: Integrate the derivative part directly.
λ∫ax2+bx+c2ax+bdx=2λax2+bx+c
since the top is exactly the derivative of what is under the root (u-substitution with u=ax2+bx+c). …
Common Mistakes
Mistake 1: Trying a single u-substitution for the whole numerator.
Why it's wrong: u=ax2+bx+c only absorbs the part of the numerator proportional to 2ax+b; the leftover constant term still has an x hidden in du, so a naive substitution leaves a stray x. Correct approach: split px+q=λ(2ax+b)+μ first, and handle the μ piece separately by completing the square.
Mistake 2: Mismatching the coefficients when solving for λ,μ.
Why it's wrong: forgetting the leading coefficient a (using 2x+… instead of 2ax+b) gives the wrong λ and a derivative piece that doesn't integrate to 2λradicand. Correct approach: always differentiate the actual radicand, then equate coefficients of x and of 1. …
Showing the 12 most recent of 51 on this concept.
- AP EAPCET 2023Set eng-2023-05-17-AN1 markMCQQ.If ∫1+x2x3dx=A(1+x2)3/2+B(1+x2)1/2+C, then A+B= (A) 2/3 (B) −2/3 (C) 1/3 (D) −1/3
›Reveal solutionSolution
The substitution u=1+x2 turns the integral into a simple power-rule computation, giving A=1/3 and B=−1, so A+B=−2/3.
Concept and Intuition
Whenever the integrand has an odd power of x alongside a function of x2 (here 1+x2), substituting u=1+x2 (so du=2xdx) converts the odd-power part into a polynomial in u, making the integral elementary.
Step-by-Step Solution
- Let u=1+x2, du=2xdx, and x2=u−1.
- x3dx=x2⋅xdx=(u−1)⋅2du.
- ∫1+x2x3dx=∫u(u−1)⋅2du=21∫(u1/2−u−1/2)du.
- =21(32u3/2−2u1/2)+C=31u3/2−u1/2+C. …
- AP EAPCET 2025Set eng-2025-05-23-AN1 markMCQQ.If ∫2cosx+3sinx+4dx=32f(x)+c, then f(32π)= (A) 12π (B) 8π (C) 125π (D) 85π
›Reveal solutionSolution
This is a Weierstrass (t=tan(x/2)) substitution problem for a linear combination of sine and cosine plus a constant in the denominator. Evaluating f at the given point gives 125π, option (C).
Concept and Intuition
Whenever the denominator mixes sinx, cosx and a constant, the universal substitution t=tan(x/2) (with cosx=1+t21−t2, sinx=1+t22t, dx=1+t22dt) converts the trigonometric denominator into a plain quadratic in t, reducing the whole problem to a standard ∫quadraticdt that integrates to an arctangent.
Step-by-Step Solution
- Substitute: denominator becomes
2⋅1+t21−t2+3⋅1+t22t+4=1+t22−2t2+6t+4+4t2=1+t22t2+6t+6.
- The integral becomes ∫(2t2+6t+6)/(1+t2)2dt/(1+t2)=∫2t2+6t+62dt=∫t2+3t+3dt.
- Complete the square: t2+3t+3=(t+23)2+43, so ∫(t+23)2+43dt=3/21arctan(3/2t+3/2)+c=32arctan(32t+3)+c. …
- AP EAPCET 2026Set eng-2026-05-14-FN1 markMCQQ.If ∫(x+5)x−5dx=152x−5f(x)+c, then f(6)= (A) 5 (B) 20 (C) 100 (D) 53
›Reveal solutionSolution
Substituting u=x−5 turns the integral into a simple power-rule computation; matching it to the given form and evaluating f at x=6 gives 53.
Concept and Intuition
An integrand with x−a multiplying a linear expression in x is best handled by substituting u=x−a, which converts everything into pure powers of u that integrate directly via the power rule. After integrating, we factor the result to match the given answer template and read off f(x).
Step-by-Step Solution
- Let u=x−5, so x=u+5, and x+5=u+10. Also dx=du.
- The integral becomes ∫(u+10)udu=∫(u3/2+10u1/2)du.
- Integrate term by term: ∫u3/2du=52u5/2, and ∫10u1/2du=10×32u3/2=320u3/2.
- So the integral =52u5/2+320u3/2+c.
- Factor out 152u3/2 (the common factor, chosen to match the given form's 152): 52u5/2=152u3/2(3u) and 320u3/2=152u3/2(50). So the integral =152u3/2(3u+50)+c=152u1/2⋅u(3u+50)+c. …
- AP EAPCET 2022Set eng-2022-07-05-FN1 markMCQQ.∫(x−3)4/5(x+1)6/5dx= (A) 455x+1x−3+C (B) 45(x−3x+1)1/5+C (C) 51(x+1x−3)1/5+C (D) 45(x+4x−3)4/5+C
›Reveal solutionSolution
Splitting off (x+1)2 turns the integrand into a pure power of t=x+1x−3, giving 45(x+1x−3)1/5+C.
Concept and Intuition
When an integrand has the form (x−a)p(x−b)q with p+q an integer (here 54+56=2), factoring out (x−b)p+q and substituting t=x−bx−a collapses the whole thing to a simple power of t — a standard trick for these "unequal fractional exponent" integrals.
Step-by-Step Solution
- (x−3)4/5(x+1)6/5=(x+1)2[x+1x−3]4/5 (factoring out (x+1)4/5+6/5=(x+1)2).
- So the integrand is (x+1)−2[x+1x−3]−4/5.
- Let t=x+1x−3. Then dxdt=(x+1)2(x+1)−(x−3)=(x+1)24, so (x+1)−2dx=4dt.
- The integral becomes 41∫t−4/5dt=41⋅1/5t1/5+C=45t1/5+C. …
- AP EAPCET 2022Set eng-2022-07-06-AN1 markMCQQ.∫(sin2x+sin−3xcos5x)3cos4xdx= (A) 51(1+cot5x)−2+C (B) 101(1+cot2x)−5+C (C) 101(1+cot5x)−2+C (D) 51(1+cot5x)−5+C
›Reveal solutionSolution
Factoring sin2x out of the denominator turns it into sin2x(1+cot5x), and the substitution t=1+cot5x makes the whole integral a simple power-rule integration, giving 101(1+cot5x)−2+C.
Concept and Intuition
Integrals with mixed powers of sinx and cosx in odd/negative combinations often simplify beautifully once you factor out a common power to expose a (1+cotnx) or (1+tannx) structure — this is exactly the kind of expression whose derivative (via chain rule) reproduces cotn−1xcsc2x, matching what's left over in the integrand.
Step-by-Step Solution
- Denominator: sin2x+sin−3xcos5x. Factor out sin2x: =sin2x[1+sin5xcos5x]=sin2x(1+cot5x).
- So the full denominator cubed: [sin2x(1+cot5x)]3=sin6x(1+cot5x)3.
- Integrand: sin6x(1+cot5x)3cos4x=sin4xcos4x⋅sin2x1⋅(1+cot5x)−3=cot4xcsc2x(1+cot5x)−3.
- Substitute t=1+cot5x. Then dxdt=5cot4x⋅(−csc2x)=−5cot4xcsc2x, so cot4xcsc2xdx=−5dt. …
- AP EAPCET 2022Set eng-2022-07-07-AN1 markMCQQ.∫x+x2+2dx= (A) 23(x+x+2)3/2−2(x+x2+2)1/4+C (B) 31(x+x2+2)3/2−2(x+x2+2)1/4+C (C) (x+x2+2)−3/2−2(x+x2+2)−1/2+C (D) 3x+x2+2(x+x2+2)2−6+C
›Reveal solutionSolution
The substitution t=x+x2+2 rationalises the nested radical; the resulting antiderivative, written as a single fraction, matches option (D). Answer: option (D).
Concept and Intuition
Integrals containing x+x2+a2 are a classic signal to substitute t equal to that whole expression — it converts the awkward nested square root into simple powers of t, because x and x2+a2 can both be written as clean rational/linear functions of t.
Step-by-Step Solution
- Let t=x+x2+2. Then x2+2=t−x; squaring, x2+2=t2−2tx+x2⇒2=t2−2tx⇒x=2tt2−2.
- Then x2+2=t−x=t−2tt2−2=2t2t2−t2+2=2tt2+2.
- Differentiate t w.r.t. x: dxdt=1+x2+2x=x2+2x2+2+x=x2+2t=(t2+2)/(2t)t=t2+22t2, so dx=2t2t2+2dt.
- Substitute into the integral: ∫tdx=∫t1/2⋅2t2t2+2dt=21∫(t1/2+2t−3/2)dt.
- Integrate: 21[32t3/2−4t−1/2]+C=31t3/2−2t−1/2+C. …
- AP EAPCET 2025Set eng-2025-05-22-FN1 markMCQQ.∫x2x4+x2+1x4−1dx= (A) x2x4+x2+1+c (B) xx4+x2+1+c (C) 2xx4+x2+1+c (D) x4x4+x2+1+c
›Reveal solutionSolution
Differentiating the candidate xx4+x2+1 reproduces the given integrand exactly, confirming it as the antiderivative.
Concept and Intuition
When an integrand looks like it could come from a quotient rule (a square root over a power of x), it is often faster to differentiate a plausible candidate of that shape and check, rather than search for a substitution from scratch.
Step-by-Step Solution
- Try g(x)=xx4+x2+1=xN where N=x4+x2+1.
- N′=2x4+x2+14x3+2x=Nx(2x2+1).
- Quotient rule: g′(x)=x2N′x−N=x2Nx2(2x2+1)−N=Nx2x2(2x2+1)−N2.
- N2=x4+x2+1, so the numerator is x2(2x2+1)−(x4+x2+1)=2x4+x2−x4−x2−1=x4−1.
- So g′(x)=x2x4+x2+1x4−1 — exactly the given integrand. …
- AP EAPCET 2026Set eng-2026-05-15-FN1 markMCQQ.∫10+sin2xcosx−sinxdx= (A) 21log(10+sin2x)+c (B) 31log(10+sin2x)+c (C) 31Tan−1(3sinx+cosx)+c (D) 31Tan−1(10+sin2x)+c
›Reveal solutionSolution
The numerator cosx−sinx is exactly d(sinx+cosx), and the denominator rewrites in terms of u=sinx+cosx via sin2x=u2−1. That collapses the integral to a standard ∫du/(a2+u2) arctangent form. Answer: 31Tan−1(3sinx+cosx)+c.
Concept and Intuition
Whenever an integrand contains both sinx−cosx (or cosx−sinx) and sin2x, it is worth trying u=sinx+cosx (or sinx−cosx) as the substitution, because u2=1±sin2x links the two.
Step-by-Step Solution
- Let u=sinx+cosx. Then du=(cosx−sinx)dx — this is exactly the numerator times dx.
- Also u2=sin2x+cos2x+2sinxcosx=1+sin2x, so sin2x=u2−1.
- Denominator: 10+sin2x=10+u2−1=9+u2.
- The integral becomes ∫9+u2du=31Tan−1(3u)+c. …
- AP EAPCET 2023Set eng-2023-05-18-FN1 markMCQQ.If ∫x(1−x3)2−1dx=32g(f(x))+c, then (A) f(x)=x, g(x)=sin−1x (B) f(x)=x3/2, g(x)=sin−1x (C) f(x)=x3/2, g(x)=cos−1x (D) f(x)=x, g(x)=cos−1x
›Reveal solutionSolution
A substitution u=x3/2 turns the integral into the standard ∫du/1−u2 form, giving f(x)=x3/2 and g=sin−1.
Concept and Intuition
The presence of xdx alongside x3=(x3/2)2 inside a square root strongly signals the substitution u=x3/2 (its derivative is proportional to x, exactly what's needed to absorb the leftover xdx). Once substituted, the integral collapses to the standard arcsine form.
Step-by-Step Solution
- Let u=x3/2. Then du=23x1/2dx=23xdx, so xdx=32du.
- Also, u2=x3, so 1−x3=1−u2.
- Substitute into the integral: ∫x(1−x3)−1/2dx=∫32⋅1−u2du=32∫1−u2du.
- This is the standard form: ∫1−u2du=sin−1u+c.
- So the integral =32sin−1(u)+c=32sin−1(x3/2)+c. …
- AP EAPCET 2026Set eng-2026-05-14-FN1 markMCQQ.∫(x5+1)6/5dx= (A) 5x5+11+c (B) x5x5+1+c (C) 5x5+1x+c (D) 5x5+1+c
›Reveal solutionSolution
Recognizing the integrand as the derivative of 5x5+1x (verified by direct differentiation) gives the antiderivative immediately.
Concept and Intuition
For integrals of the form ∫(xn+1)(n+1)/ndx, a useful trick is to guess that the antiderivative looks like (xn+1)1/nx (a ratio designed to make the product-rule differentiation collapse nicely), and then verify by differentiating it — if it reproduces the integrand exactly, we're done. This is often faster than a substitution for this particular family.
Step-by-Step Solution
- Guess the antiderivative g(x)=(x5+1)1/5x=x(x5+1)−1/5.
- Differentiate using the product rule: g′(x)=(x5+1)−1/5+x⋅(−51)(x5+1)−6/5⋅5x4.
- Simplify the second term: x⋅(−51)(5x4)(x5+1)−6/5=−x5(x5+1)−6/5.
- So g′(x)=(x5+1)−1/5−x5(x5+1)−6/5.
- Factor out (x5+1)−6/5: g′(x)=(x5+1)−6/5[(x5+1)−x5]=(x5+1)−6/5×1=(x5+1)−6/5. …
- AP EAPCET 2026Set eng-2026-05-15-AN1 markMCQQ.If ∫x5e−4x3dx=481e−4x3f(x)+c, then f(x)= (A) −2x3−1 (B) −4x3−1 (C) −2x2+1 (D) 4x3+1
›Reveal solutionSolution
Substituting u=x3 converts the integral into a simple integration-by-parts problem ∫ue−4udu; matching the result to the given form yields f(x)=−4x3−1.
Concept and Intuition
The presence of x5 alongside e−4x3 is a strong hint to substitute u=x3, since then x2dx (part of du) combines with the remaining x3=u to leave a clean polynomial-times-exponential integral, solvable by the standard integration-by-parts reduction formula for ∫uekudu.
Step-by-Step Solution
- Let u=x3, so du=3x2dx⇒x2dx=3du.
- Rewrite x5e−4x3dx=x3⋅x2e−4x3dx=ue−4u⋅3du.
- So the integral becomes 31∫ue−4udu.
- Integrate by parts with first function u, second e−4u: ∫ue−4udu=u⋅(−4e−4u)−∫(−4e−4u)du=−4ue−4u−161e−4u. …
- AP EAPCET 2025Set eng-2025-05-21-AN1 markMCQQ.If ∫(x−1)3/2(x−3)1/2dx=f(x)+c then f(−1)−f(0)= (A) −3 (B) −4 (C) −2 (D) −1
›Reveal solutionSolution
A classic "divide by (x−1)2 and substitute t=(x−3)/(x−1)" integral. It reduces to t, giving f(x)=(x−3)/(x−1), and then f(−1)−f(0)=−1.
Concept and Intuition
When an integrand has two linear factors under different fractional powers whose exponents sum to an integer (here 3/2+1/2=2), factor out (x−1)2 from the denominator and express the rest as a function of the ratio x−1x−3. This ratio then becomes a natural single substitution variable.
Step-by-Step Solution
- Write the denominator as
(x−1)3/2(x−3)1/2=(x−1)2⋅(x−1)1/2(x−3)1/2=(x−1)2x−1x−3.
- So the integral is ∫(x−1)2x−1x−3dx.
- Let t=x−1x−3=1−x−12. Then dxdt=(x−1)22, i.e. (x−1)2dx=2dt.
- The integral becomes ∫tdt/2=21⋅2t+c=t+c=x−1x−3+c. …
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