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← JEE Main 2022 · 29 Jun · Shift 2
MathematicsInteger+4 / -1Question 26 of 90

JEE Main 2022 · 29 Jun · Shift 2, Mathematics question 26

Let ff and gg be twice differentiable even functions on (−2,2)(-2,2) such that f(14)=0f\left(\frac14\right)=0, f(12)=0f\left(\frac12\right)=0, f(1)=1f(1)=1 and g(34)=0g\left(\frac34\right)=0, g(1)=2g(1)=2. Then, the minimum number of solutions of f(x)g′′(x)+f′(x)g′(x)=0f(x)g''(x)+f'(x)g'(x)=0 in (−2,2)(-2,2) is equal to ______.

Answer and worked solution

Official answer: 4

Rewrite. The equation is (fg′)′=0(fg')'=0. Let h=fg′h=fg'.

Zeros of h. f=0f=0 at ±14,±12\pm\frac14,\pm\frac12; g′(0)=0g'(0)=0 since gg is even. Five zeros, so by Rolle h′h' has at least 4.

Answer: 4