Sign in
12thPass logo
New chatPYQ LibraryDoubtsRank report
Sign in to see Recents

Your guest activity stays on this device

Sign in to save progress →
Sign in

Definite Integration question

2022 · 30 Jun · Shift 1 · Q37
Guest · filters and generic practice availableBrowsing as a guest · PYQ filters and generic practice are available. Sign in only for personalised features and saved progress.
  1. PYQ Library
  2. /JEE Main
  3. /Mathematics
  4. /Definite Integration
  5. /2022 · 30 Jun · Shift 1 · Q37

Definite Integration question

2022 · 30 Jun · Shift 1 · Q37

JEE MainMathematicsDefinite IntegrationNumerical+4 / −1
Let f(t)=∫0tex3(x8(x6+2x3+2)2)dxf(t) = \int\limits_0^t {{e^{{x^3}}}\left( {{{{x^8}} \over {{{({x^6} + 2{x^3} + 2)}^2}}}} \right)dx}f(t)=0∫t​ex3((x6+2x3+2)2x8​)dx. If f(1)+f′(1)=αe−16f(1) + f'(1) = \alpha e - {1 \over 6}f(1)+f′(1)=αe−61​, then the value of 150 α\alphaα is equal to ‾\underline{\hspace{2cm}}​.
Numerical answer
View written solutionFree

Correct answer: 16

  1. Given function
f(t)=∫0tex3(x8(x6+2x3+2)2) dxf(t)=\int_0^t e^{x^3}\left(\frac{x^8}{(x^6+2x^3+2)^2}\right)\,dxf(t)=∫0t​ex3((x6+2x3+2)2x8​)dx

We need to find f(1)+f′(1)f(1)+f'(1)f(1)+f′(1) and compare it with

αe−16.\alpha e-\frac16.αe−61​.
  1. Simplify the integrand

Notice that

x6+2x3+2=(x3+1)2+1.x^6+2x^3+2=(x^3+1)^2+1.x6+2x3+2=(x3+1)2+1.

Let

u=x3  ⟹  dν=3x2dx.u=x^3 \implies d\nu=3x^2dx.u=x3⟹dν=3x2dx.

But the given integrand has x8dx=x6x2dx=(x3)2x2dx=ν2x2dxx^8dx=x^6x^2dx=(x^3)^2x^2dx=\nu^2x^2dxx8dx=x6x2dx=(x3)2x2dx=ν2x2dx. So,

x8dx=ν2dν3.x^8dx=\nu^2\frac{d\nu}{3}.x8dx=ν23dν​.

Also,

ex3=eν,x6+2x3+2=ν2+2ν+2.e^{x^3}=e^{\nu}, \qquad x^6+2x^3+2=\nu^2+2\nu+2.ex3=eν,x6+2x3+2=ν2+2ν+2.

Hence

f(t)=13∫0t3eνν2(ν2+2ν+2)2 dν.f(t)=\frac13\int_0^{t^3} \frac{e^{\nu}\nu^2}{(\nu^2+2\nu+2)^2}\,d\nu.f(t)=31​∫0t3​(ν2+2ν+2)2eνν2​dν.

Now observe:

ddν(eνν2+2ν+2)=eν(ν2+2ν+2)−eν(2ν+2)(ν2+2ν+2)2=eνν2(ν2+2ν+2)2.\frac{d}{d\nu}\left(\frac{e^{\nu}}{\nu^2+2\nu+2}\right) =\frac{e^{\nu}(\nu^2+2\nu+2)-e^{\nu}(2\nu+2)}{(\nu^2+2\nu+2)^2} =\frac{e^{\nu}\nu^2}{(\nu^2+2\nu+2)^2}.dνd​(ν2+2ν+2eν​)=(ν2+2ν+2)2eν(ν2+2ν+2)−eν(2ν+2)​=(ν2+2ν+2)2eνν2​.

Therefore,

f(t)=13[eνν2+2ν+2]0t3=13(et3t6+2t3+2−12).f(t)=\frac13\left[\frac{e^{\nu}}{\nu^2+2\nu+2}\right]_0^{t^3} =\frac13\left(\frac{e^{t^3}}{t^6+2t^3+2}-\frac{1}{2}\right).f(t)=31​[ν2+2ν+2eν​]0t3​=31​(t6+2t3+2et3​−21​).

So,

f(t)=et33(t6+2t3+2)−16.f(t)=\frac{e^{t^3}}{3(t^6+2t^3+2)}-\frac16.f(t)=3(t6+2t3+2)et3​−61​.
  1. Compute f(1)f(1)f(1)

At t=1t=1t=1,

t6+2t3+2=1+2+2=5.t^6+2t^3+2=1+2+2=5.t6+2t3+2=1+2+2=5.

Thus,

f(1)=e15−16.f(1)=\frac{e}{15}-\frac16.f(1)=15e​−61​.
  1. Compute f′(1)f'(1)f′(1)

By the Fundamental Theorem of Calculus,

f′(t)=et3t8(t6+2t3+2)2.f'(t)=e^{t^3}\frac{t^8}{(t^6+2t^3+2)^2}.f′(t)=et3(t6+2t3+2)2t8​.

Therefore,

f′(1)=e⋅1(1+2+2)2=e25.f'(1)=e\cdot \frac{1}{(1+2+2)^2}=\frac{e}{25}.f′(1)=e⋅(1+2+2)21​=25e​.
  1. Add f(1)+f′(1)f(1)+f'(1)f(1)+f′(1)
f(1)+f′(1)=(e15−16)+e25=e(115+125)−16.f(1)+f'(1)=\left(\frac{e}{15}-\frac16\right)+\frac{e}{25} = e\left(\frac{1}{15}+\frac{1}{25}\right)-\frac16.f(1)+f′(1)=(15e​−61​)+25e​=e(151​+251​)−61​.

Now,

115+125=5+375=875.\frac{1}{15}+\frac{1}{25}=\frac{5+3}{75}=\frac{8}{75}.151​+251​=755+3​=758​.

So,

f(1)+f′(1)=8e75−16.f(1)+f'(1)=\frac{8e}{75}-\frac16.f(1)+f′(1)=758e​−61​.

Comparing with

αe−16,\alpha e-\frac16,αe−61​,

we get

α=875.\alpha=\frac{8}{75}.α=758​.

Hence,

150α=150⋅875=16.150\alpha=150\cdot \frac{8}{75}=16.150α=150⋅758​=16.
  1. Comparison with stored answer

Derived answer: 161616

Stored correct answer: 161616

They match.

PreviousNext

More from Definite Integration

  • Let f : R → R be a continuous function. Then x→4π​lim​x2−16π2​4π​2∫sec2x​f(x)dx​ is equal to :2021 · MCQ
  • Let Jn,m​=0∫21​​xm−1xn​dx, ∀ n > m and n, m ∈ N. Consider a matrix A=[aij​]3×3​ where aij​={j6+i,3​−ji+3,3​,0,​i≤ji>j​…2021 · MCQ
  • The function f(x), that satisfies the condition f(x)=x+0∫π/2​sinx.cosyf(y)dy, is :2021 · MCQ
  • Let f : R → R be a continuous function such that f(x) + f(x + 1) = 2, for all x ∈ R. If I1​=0∫8​f(x)dx and I2​=−1∫3​f(x)dx, then the value of I1 + 2I2 is equal to ​…2021 · Numerical
  • If the normal to the curve y(x) = 0∫x​(2t2−15t+10)dt at a point (a, b) is parallel to the line x + 3y =− 5, a > 1, then the value of | a + 6b | is equal to ​.2021 · Numerical
  • Consider the integral I=∫010​ex−1[x]e[x]​dx, where [x] denotes the greatest integer less than or equal to x. Then the value of I is equal to :2021 · MCQ
  • Let P(x) = x2 + bx + c be a quadratic polynomial with real coefficients such that ∫01​P(x)dx= 1 and P(x) leaves remainder 5 when it is divided by (x − 2). Then the value of 9(b + c) is equal to :2021 · MCQ
  • Which of the following statements is correct for the function g(α) for α∈ R such that g(α)=6π​∫3π​​cosαx+sinαxsinαx​dx2021 · MCQ