Q.

For every twice differentiable function f:2,2 with f02+f102=85  which of the  Following statement(s) is (are) TRUE?

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a

There exists x04,0 such that     f1x01

b

limxfx=1

c

There exist r,s, where r<s, such that f is one-one on the open interval r.s

d

There exists α4,4 such that  fα+f11α=0 and f1α0

answer is A, B, D.

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Detailed Solution

ƒ(x) can't be constant throughout the domain. Hence we can find x  (r, s) such that ƒ(x) is one-one  

Option (A) is true

f1x0=f0f441

Option (B) is true

fx=sin85x satisfies the given condition  but limxsin85x but does not exist.

Option (C) is not true. 

Let gx=f2x+f1x2

Since f1x11 and fx12 it gives gx15for some x14,0

g(0)=85g(x) has maxima in x1,x2 say at αg1(α)=0.

 2f1(α)f(α)+f11(α)=0

 If f1(α)=0g(α)=f2(α)=85 not possible f(α)+f11α=0 for some αx1,x2(-4,4)

Option (D) is correct

 

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