The function f:R→R satisfies f(x2)f′′(x)=f′(x)f′(x2)∀x∈R, given that f(1)=1 and f′′′(1)=8, then
A
f′(1)=2
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B
f′′(1)=4
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C
f′(1)=4
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D
f′′(1)=2
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Solution
The correct options are Af′(1)=2 Bf′′(1)=4 Let f′(1)=a,f′′(1)=b Put x=1⇒f(1)f′′(1)=f′(1)f′(1) b=a2 differentiating again f′(x2).2xf′′(x)+f(x2)f′′′(x)=f′(x)f′′(x2).2x+f′(x2).f′′(x) Put x=1 2ab+8=ab+2ab⇒ab=8 So, a=2,b=4