Skip to content
dronacharya.ai
← JEE Main 2022 · 27 Jul · Shift 2
MathematicsInteger+4 / -1Question 28 of 90

JEE Main 2022 · 27 Jul · Shift 2, Mathematics question 28

Let ff be a differentiable function satisfying f(x)=23∫03f(λ2x3)dλf(x)=\dfrac2{\sqrt3}\displaystyle\int_0^{\sqrt3}f\left(\frac{\lambda^2x}3\right)d\lambda, x>0x>0 and f(1)=3f(1)=\sqrt3. If y=f(x)y=f(x) passes through the point (α,6)(\alpha,6), then α\alpha is equal to ______.

Answer and worked solution

Official answer: 12

Substitute t=λ2x3t=\frac{\lambda^2x}3: xf(x)=∫0xf(t)tdt\sqrt xf(x)=\int_0^x\frac{f(t)}{\sqrt t}dt.

Differentiate. f2x+xf′=fx\frac f{2\sqrt x}+\sqrt xf'=\frac f{\sqrt x}, so f=cx=3xf=c\sqrt x=\sqrt{3x}.

Solve 3α=6\sqrt{3\alpha}=6: α=12\alpha=12.

Answer: 12