arthham

JEE Advanced 2014 · Integrals

The value of ∫014x3{d2dx2(1−x2)5}dx\int_{0}^{1} 4x^{3}\left\{\frac{d^{2}}{dx^{2}}\left(1-x^{2}\right)^{5}\right\}dx is

Answer: 22

Watch this solved on the board The full walkthrough, written out a line at a time with narration explaining each step as it appears. Pause anywhere and ask why a line is there. Free to watch

Or read the worked solution below. Jump to the steps ↓

Written solution

The value of ∫₀¹ 4x³{d²/dx²(1-x²)⁵}dx is

I=∫014x3  d2dx2 ⁣[(1−x2)5]dxI = \displaystyle\int_{0}^{1} 4x^{3}\;\dfrac{d^{2}}{dx^{2}}\!\left[(1-x^{2})^{5}\right]dx

To find: I\text{To find: } I

g(x)=(1−x2)5,g(1)=0, g(0)=1g(x) = (1-x^2)^5, \quad g(1)=0,\ g(0)=1

g′(x)=−10x(1−x2)4,g′(1)=0, g′(0)=0g'(x) = -10x(1-x^2)^4, \quad g'(1)=0,\ g'(0)=0

I=[4x3g′]01−∫0112x2g′ dxI = \Big[4x^3 g'\Big]_{0}^{1} - \int_{0}^{1} 12x^2 g'\,dx

I=[4x3g′]01−[12x2g]01+∫0124x g dxI = \Big[4x^3 g'\Big]_{0}^{1} - \Big[12x^2 g\Big]_{0}^{1} + \int_{0}^{1} 24x\,g\,dx

g(1)=g′(1)=0;x3=x2=0 at x=0g(1)=g'(1)=0; \quad x^3=x^2=0 \text{ at } x=0

⇒[4x3g′]01=[12x2g]01=0\Rightarrow \Big[4x^3 g'\Big]_{0}^{1} = \Big[12x^2 g\Big]_{0}^{1} = 0

I=∫0124x(1−x2)5 dxI = \int_{0}^{1} 24x(1-x^2)^5\,dx

u=1−x2  ⇒  x dx=−du2u = 1-x^2 \;\Rightarrow\; x\,dx = -\dfrac{du}{2}

x=0⇒u=1,x=1⇒u=0x=0\Rightarrow u=1, \quad x=1\Rightarrow u=0

I=24⋅12∫01u5 du=12[u66]01I = 24\cdot\dfrac{1}{2}\int_{0}^{1} u^{5}\,du = 12\left[\dfrac{u^{6}}{6}\right]_{0}^{1}

I=12⋅16=2I = 12\cdot\dfrac{1}{6} = 2

I=2\boxed{I = 2}

More from Integrals

All 55 Integrals questions →

Integrals: formulas and what the chapter covers →