Q.β« π
π ππ(π+ππ) π π equals
(A) β 1 2π₯2 β1 + π₯4 + π
(B) 1 2π₯ β1 + π₯4 + π
(C) β 1 4π₯ β1 + π₯4 + π
(D) 1 4π₯2 β1 + π₯4 + π
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π Start your 14-day free trial to unlock the full solution βConcept understanding β U Substitution
U Substitution: The Reverse Chain Rule
The chain rule differentiates composite functions: the derivative of sin(x2) is cos(x2)β 2x β differentiate the outer function, then multiply by the derivative of the inside. Integration asks the reverse: given cos(x2)β 2x, find the original function. That's what u substitution does β 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:
β«2xcos(x2)dx
Here 2x is the derivative of x2, and x2 is the inside of cos(x2). Let u=x2, so du=2xdx:
β«cos(u)du=sin(u)+C=sin(x2)+C
Check: the derivative of sin(x2) is cos(x2)β 2x.
The Precise Statement
β«f(g(x))β gβ²(x)dx=β«f(u)duwhereΒ u=g(x),du=gβ²(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 gβ²(x) also appears (possibly up to a constant factor).
- Set u=g(x), compute du=gβ²(x)dx.
- Rewrite the entire integral in u and du β 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 β rare).
A Second Example (with a constant factor)
Evaluate β«xx2+1βdx. Let u=x2+1, so xdx=21βdu:
β«uββ 21βdu=21ββ 32βu3/2+C=31β(x2+1)3/2+C
When Does It Work?
When the integrand is something times the derivative of something inside. Common patterns:
- xβ f(x2) β derivative of x2 is 2x, so u=x2
- eg(x)β gβ²(x) β derivative of g(x) appears
- g(x)gβ²(x)β β leads to logβ£g(x)β£ β¦
Key idea: factor x4 out of the root, then the leftover is a perfect differential.
Since 1+x4β=x21+xβ4β, the integrand becomes
x31+x4β1β=x3β x21+xβ4β1β=1+xβ4βxβ5β.
Let u=1+xβ4, so du=β4xβ5dx, i.e. xβ5dx=β41βdu:
β«1+xβ4βxβ5dxβ=β41ββ«uβ1/2du=β41ββ 2uβ=β21βuβ. β¦
Pull x4 out of the square root and substitute u=1+xβ4; the integral equals β2x21+x4ββ+c, which is option (A).
We want
β«x31+x4βdxβ.
Why factor x4 out? The derivative of x4 is 4x3, so a bare u=x4 substitution wants an x3 in the numerator β but here x3 sits in the denominator. Pulling x4 out of the root converts the problem into one where the exact needed differential does appear.
1. Rewrite the integrand
1+x4β=x4(1+x41β)β=x21+xβ4β(x>0).
So
x31+x4β1β=x3β x21+xβ4β1β=1+xβ4βxβ5β.
2. Substitute
Let u=1+xβ4. Then du=β4xβ5dx, so xβ5dx=β41βdu. Notice the integrand contains exactly xβ5dx times uβ1β:
β«1+xβ4βxβ5dxβ=β«uββ41βduβ=β41ββ«uβ1/2du. β¦
Method: Substitution when a high power of x blocks the obvious u
Use this for integrands like xm1+xnβ1β where a direct substitution u=1+xn fails because the needed xnβ1 sits in the denominator, not the numerator.
Steps
Step 1: Factor the highest power of x out of the root.
1+xnβ=xn(1+xβn)β=xn/21+xβnβ(x>0).
This deliberately introduces a negative power of x, which is the differential you actually need.
Step 2: Collect all powers of x into one factor.
Rewrite the whole integrand so it reads (power of x) Γ1+xβnβ1β. The power of x should now match the derivative of xβn.
Step 3: Substitute u=1+xβn. β¦
Common Mistakes
Mistake 1: Trying u=1+x4 directly.
Why it's wrong: then du=4x3dx needs an x3 in the numerator, but here x3 is in the denominator β the substitution leaves stray x's. Correct approach: factor x4 out of the root first to manufacture the xβ5dx that u=1+xβ4 needs.
Mistake 2: Mishandling x4β=x2 signs.
Why it's wrong: x4β=x2 is fine, but pulling out x-powers carelessly (e.g. x4β=x) corrupts the algebra. Correct approach: track exponents precisely β x4β=x2, and 1+xβ4β=1+x4β/x2. β¦
Showing the 12 most recent of 51 on this concept.
- AP EAPCET 2026Set eng-2026-05-13-AN1 markMCQQ.β«x2(x4+1)3/4dxβ= (A) (1+x41β)3/4+c (B) (1+x61β)1/2+c (C) β(1+x41β)β1/4+c (D) β(1+x41β)1/4+c
βΊReveal solutionSolution
Pulling x4 out from under the radical and substituting t=1+xβ4 reduces the integral to a simple power rule, giving β(1+1/x4)1/4+c.
Concept and Intuition
When the integrand has (xn+1)p, it often helps to factor out the highest power of x from inside the bracket so that a substitution like t=1+xβn produces a clean differential matching the rest of the integrand.
Step-by-Step Solution
- Write (x4+1)3/4=(x4(1+x41β))3/4=x3(1+x41β)3/4.
- So x2(x4+1)3/41β=x2β x3(1+x41β)3/41β=x5(1+x41β)3/41β=xβ5(1+xβ4)β3/4.
- Let t=1+xβ4. Then dt=β4xβ5dx, so xβ5dx=β4dtβ. β¦
- AP EAPCET 2024Set eng-2024-05-22-FN1 markMCQQ.β«1+x8x3tanβ1x4βdx= (A) 8(tanβ1(x4))2β+c (B) 3(tanβ1(x4))3β+c (C) 4(tanβ1(x4))2β+c (D) 2(tanβ1(x4))2β+c
βΊReveal solutionSolution
A double substitution (first u=x4, then v=tanβ1u) turns this into a trivial β«vdv. Answer: 8(tanβ1x4)2β+c.
Concept and Intuition
The presence of x3dx alongside x4 inside the arctan and x8=(x4)2 in the denominator is a strong signal to substitute u=x4 first. After that, the structure tanβ1uβ 1+u2duβ is exactly of the form "function times its own derivative," solved by a second substitution.
Step-by-Step Solution
- Let u=x4, so du=4x3dxβx3dx=4duβ.
- The integral becomes β«1+u2tanβ1uββ 4duβ=41ββ«1+u2tanβ1uβdu. β¦
- AP EAPCET 2026Set eng-2026-05-15-FN1 markMCQQ.β«(1+sinx)4cos3xβdx= (A) β5(1+sinx)5cos4xβ+c (B) 5(1+sinx)5cos4xβ+c (C) 4(1+sinx)4cos4xβ+c (D) β4(1+sinx)4cos4xβ+c
βΊReveal solutionSolution
Factor cos3x using cos2x=(1βsinx)(1+sinx) and substitute t=sinx; the resulting antiderivative can equivalently be written in the cos4x/(1+sinx)4 form given in the options (they differ only by an added constant). Answer: β4(1+sinx)4cos4xβ+c.
Concept and Intuition
Integrals of cosoddx over powers of (1+sinx) are handled by peeling off one factor of cosx to pair with dx (making d(sinx)) and expressing the remaining even power of cosx in terms of sinx. Since the MCQ options are phrased in terms of cos4x rather than sinx directly, it is often faster (and safer against sign traps) to guess-and-check an antiderivative of that shape by differentiating a general form Acos4x(1+sinx)βn and matching powers/coefficients β this is exactly how the printed option is confirmed.
Step-by-Step Solution
- cos3x=cosxβ cos2x=cosx(1βsin2x)=cosx(1βsinx)(1+sinx).
- Integrand =(1+sinx)4cosx(1βsinx)(1+sinx)β=(1+sinx)3cosx(1βsinx)β.
- Let t=sinx, dt=cosxdx: I=β«(1+t)31βtβdt. Writing 1βt=2β(1+t): I=β«((1+t)32ββ(1+t)21β)dt=β(1+t)21β+1+t1β+c=(1+t)2tβ+c.
- So I=(1+sinx)2sinxβ+c is one valid closed form. β¦
- AP EAPCET 2022Set eng-2022-07-05-FN1 markMCQQ.β«(xβ3)4/5(x+1)6/5dxβ= (A) 45β5x+1xβ3ββ+C (B) 45β(xβ3x+1β)1/5+C (C) 51β(x+1xβ3β)1/5+C (D) 45β(x+4xβ3β)4/5+C
βΊReveal solutionSolution
Splitting off (x+1)2 turns the integrand into a pure power of t=x+1xβ3β, giving 45β(x+1xβ3β)1/5+C.
Concept and Intuition
When an integrand has the form (xβa)p(xβb)q with p+q an integer (here 54β+56β=2), factoring out (xβb)p+q and substituting t=xβbxβaβ collapses the whole thing to a simple power of t β a standard trick for these "unequal fractional exponent" integrals.
Step-by-Step Solution
- (xβ3)4/5(x+1)6/5=(x+1)2[x+1xβ3β]4/5 (factoring out (x+1)4/5+6/5=(x+1)2).
- So the integrand is (x+1)β2[x+1xβ3β]β4/5.
- Let t=x+1xβ3β. Then dxdtβ=(x+1)2(x+1)β(xβ3)β=(x+1)24β, so (x+1)β2dx=4dtβ.
- The integral becomes 41ββ«tβ4/5dt=41ββ 1/5t1/5β+C=45βt1/5+C. β¦
- AP EAPCET 2022Set eng-2022-07-07-AN1 markMCQQ.β«x+x2+2ββdx= (A) 23β(x+x+2β)3/2β2(x+x2+2β)1/4+C (B) 31β(x+x2+2β)3/2β2(x+x2+2β)1/4+C (C) (x+x2+2β)β3/2β2(x+x2+2β)β1/2+C (D) 3x+x2+2ββ(x+x2+2β)2β6β+C
βΊReveal solutionSolution
The substitution t=x+x2+2β 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+a2β are a classic signal to substitute t equal to that whole expression β it converts the awkward nested square root into simple powers of t, because x and x2+a2β can both be written as clean rational/linear functions of t.
Step-by-Step Solution
- Let t=x+x2+2β. Then x2+2β=tβx; squaring, x2+2=t2β2tx+x2β2=t2β2txβx=2tt2β2β.
- Then x2+2β=tβx=tβ2tt2β2β=2t2t2βt2+2β=2tt2+2β.
- Differentiate t w.r.t. x: dxdtβ=1+x2+2βxβ=x2+2βx2+2β+xβ=x2+2βtβ=(t2+2)/(2t)tβ=t2+22t2β, so dx=2t2t2+2βdt.
- Substitute into the integral: β«tβdx=β«t1/2β 2t2t2+2βdt=21ββ«(t1/2+2tβ3/2)dt.
- Integrate: 21β[32βt3/2β4tβ1/2]+C=31βt3/2β2tβ1/2+C. β¦
- AP EAPCET 2025Set eng-2025-05-22-FN1 markMCQQ.β«x2x4+x2+1βx4β1βdx= (A) x2x4+x2+1ββ+c (B) xx4+x2+1ββ+c (C) 2xx4+x2+1ββ+c (D) x4x4+x2+1ββ+c
βΊReveal solutionSolution
Differentiating the candidate xx4+x2+1ββ 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+1ββ=xNβ where N=x4+x2+1β.
- Nβ²=2x4+x2+1β4x3+2xβ=Nx(2x2+1)β.
- Quotient rule: gβ²(x)=x2Nβ²xβNβ=x2Nx2(2x2+1)ββNβ=Nx2x2(2x2+1)βN2β.
- N2=x4+x2+1, so the numerator is x2(2x2+1)β(x4+x2+1)=2x4+x2βx4βx2β1=x4β1.
- So gβ²(x)=x2x4+x2+1βx4β1β β exactly the given integrand. β¦
- AP EAPCET 2022Set eng-2022-07-06-AN1 markMCQQ.β«(sin2x+sinβ3xcos5x)3cos4xβdx= (A) 51β(1+cot5x)β2+C (B) 101β(1+cot2x)β5+C (C) 101β(1+cot5x)β2+C (D) 51β(1+cot5x)β5+C
βΊReveal 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 101β(1+cot5x)β2+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 β this is exactly the kind of expression whose derivative (via chain rule) reproduces cotnβ1xcsc2x, matching what's left over in the integrand.
Step-by-Step Solution
- Denominator: sin2x+sinβ3xcos5x. Factor out sin2x: =sin2x[1+sin5xcos5xβ]=sin2x(1+cot5x).
- So the full denominator cubed: [sin2x(1+cot5x)]3=sin6x(1+cot5x)3.
- Integrand: sin6x(1+cot5x)3cos4xβ=sin4xcos4xββ sin2x1ββ (1+cot5x)β3=cot4xcsc2x(1+cot5x)β3.
- Substitute t=1+cot5x. Then dxdtβ=5cot4xβ (βcsc2x)=β5cot4xcsc2x, so cot4xcsc2xdx=β5dtβ. β¦
- AP EAPCET 2024Set eng-2024-05-18-FN1 markMCQQ.β«x55x5+1β1βdx= (A) 5x5+1β4β+c (B) 4x4(x5+1)4/5+c (C) β4x4(x5+1)4/5β+c (D) β4x5(x5+1)4/5β+c
βΊReveal solutionSolution
Rewriting the integrand to expose 1+xβ5 as the natural substitution variable solves this cleanly; the answer is β4x4(x5+1)4/5β+c.
Concept and Intuition
When an integral mixes a power of x with a root of a polynomial in x, factoring out the highest power of x from inside the root often converts the expression into a function of 1/x (or xβ5 here), whose derivative is already present elsewhere in the integrand β a clean substitution.
Step-by-Step Solution
- (x5+1)β1/5=(x5(1+xβ5))β1/5=xβ1(1+xβ5)β1/5.
- So the integrand xβ5(x5+1)β1/5=xβ6(1+xβ5)β1/5.
- Let t=1+xβ5, so dt=β5xβ6dxβxβ6dx=β5dtβ.
- Integral =β«tβ1/5(β5dtβ)=β51ββ 4/5t4/5β+c=β41βt4/5+c. β¦
- AP EAPCET 2023Set eng-2023-05-17-AN1 markMCQQ.If β«1+x2βx3βdx=A(1+x2)3/2+B(1+x2)1/2+C, then A+B= (A) 2/3 (B) β2/3 (C) 1/3 (D) β1/3
βΊReveal solutionSolution
The substitution u=1+x2 turns the integral into a simple power-rule computation, giving A=1/3 and B=β1, so A+B=β2/3.
Concept and Intuition
Whenever the integrand has an odd power of x alongside a function of x2 (here 1+x2β), 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=uβ1.
- x3dx=x2β xdx=(uβ1)β 2duβ.
- β«1+x2βx3βdx=β«uβ(uβ1)ββ 2duβ=21ββ«(u1/2βuβ1/2)du.
- =21β(32βu3/2β2u1/2)+C=31βu3/2βu1/2+C. β¦
- AP EAPCET 2021Set eng-2021-08-24-FN1 markMCQQ.If β«3xβ{1+3x4β}1/7dx=A(1+3x4β)B+C, then value of AB= ____ (A) 23β (B) 43β (C) 323β (D) 34β
βΊReveal solutionSolution
A direct substitution u=1+x4/3 turns the integral into a simple power rule, from which A and B are read off and multiplied.
Concept and Intuition
When the integrand contains x1/3 times a function of x4/3, substituting u=1+x4/3 (whose derivative involves exactly x1/3dx) is the natural simplification.
Step-by-Step Solution
- Let u=1+x4/3. Then du=34βx1/3dxβx1/3dx=43βdu.
- The integral β«x1/3(1+x4/3)1/7dx=43ββ«u1/7du.
- β«u1/7du=8/7u8/7β=87βu8/7.
- So the integral =43ββ 87βu8/7+C=3221β(1+x4/3)8/7+C. β¦
- AP EAPCET 2025Set eng-2025-05-27-FN1 markMCQQ.β«(1+xβ)xβx2βdxβ= (A) β21βxβ1+xβββ+c (B) β1+xβ1βxβββ+c (C) β21+xβ1βxβββ+c (D) 21βxβ1+xβββ+c
βΊReveal solutionSolution
Substituting t=xβ turns the surd-heavy integrand into β«(1+t)3/2(1βt)1/22dtβ, whose antiderivative is exactly β21+t1βtββ.
Concept and Intuition
When an integrand mixes xβ and xβx2β=xβ1βxβ, substituting t=xβ clears every square root of x at once, converting the whole thing into a rational-power integral in t that matches the derivative of 1+t1βtββ β a standard "recognise the derivative" pattern worth memorising for CET-style problems.
Step-by-Step Solution
- Write xβx2β=x(1βx)β=xβ1βxβ, so the integral is
I=β«(1+xβ)xβ1βxβdxβ.
- Let t=xβ, so x=t2, dx=2tdt:
I=β«(1+t)β tβ 1βt2β2tdtβ=β«(1+t)(1βt)(1+t)β2dtβ=β«(1+t)3/2(1βt)1/22dtβ.
- Let y=1+t1βtββ. Differentiating y2=1+t1βtβ: 2yyβ²=(1+t)2β(1+t)β(1βt)β=(1+t)2β2βΒ βΒ yβ²=y(1+t)2β1β=(1+t)3/2(1βt)1/2β1β. β¦
- AP EAPCET 2026Set eng-2026-05-14-FN1 markMCQQ.β«(x5+1)6/5dxβ= (A) 5x5+1β1β+c (B) x5x5+1ββ+c (C) 5x5+1βxβ+c (D) 5x5+1β+c
βΊReveal solutionSolution
Recognizing the integrand as the derivative of 5x5+1βxβ (verified by direct differentiation) gives the antiderivative immediately.
Concept and Intuition
For integrals of the form β«(xn+1)(n+1)/ndxβ, a useful trick is to guess that the antiderivative looks like (xn+1)1/nxβ (a ratio designed to make the product-rule differentiation collapse nicely), and then verify by differentiating it β 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)1/5xβ=x(x5+1)β1/5.
- Differentiate using the product rule: gβ²(x)=(x5+1)β1/5+xβ (β51β)(x5+1)β6/5β 5x4.
- Simplify the second term: xβ (β51β)(5x4)(x5+1)β6/5=βx5(x5+1)β6/5.
- So gβ²(x)=(x5+1)β1/5βx5(x5+1)β6/5.
- Factor out (x5+1)β6/5: gβ²(x)=(x5+1)β6/5[(x5+1)βx5]=(x5+1)β6/5Γ1=(x5+1)β6/5. β¦
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