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← JEE Advanced 2014 · Paper 1
MathematicsInteger+3Question 55 of 60

JEE Advanced 2014 · Paper 1, Mathematics question 55

The value of
∫014x3{d2dx2(1−x2)5}dx\int_0^14x^3\left\{\frac{d^2}{dx^2}(1-x^2)^5\right\}dx
is

Answer and worked solution

Official answer: 2

Integrate by parts twice. Let y=(1−x2)5y=(1-x^2)^5, so y′=−10x(1−x2)4y'=-10x(1-x^2)^4. Both yy and y′y' vanish at x=1x=1, and x3x^3, x2x^2 vanish at 0.
∫014x3y′′ dx=[4x3y′]01−∫0112x2y′ dx=−[12x2y]01+∫0124xy dx.\int_0^14x^3y''\,dx=\Big[4x^3y'\Big]_0^1-\int_0^112x^2y'\,dx=-\Big[12x^2y\Big]_0^1+\int_0^124xy\,dx.

Last integral.
24∫01x(1−x2)5dx=24⋅112=2.24\int_0^1x(1-x^2)^5dx=24\cdot\frac1{12}=2.

Answer: 2