JEE Advanced | 2018Set, Relation and FunctionHard

Question

Let ƒ : and g :  be two non-constant differentiable functions. If ƒ'(x) = (e(ƒ(x) – (x)))g'(x)
for all x , and ƒ(1) = g(2) = 1, then which of the following statement(s) is (are) TRUE ?

Options

A.

ƒ(2) < 1 – loge2

B.

ƒ(2) > 1 – loge2

C.

g(1) > 1 – loge2

D.

g(1) < 1 – loge2

Solution

ƒ'(x) = e(ƒ(x) – g(x)) g'(x) x
e–ƒ(x). ƒ'(x) – e–g(x)g'(x) = 0
(e-ƒ(x ) ƒ '(x) - eg(x) .g '(x))dx = C
-e -ƒ(x) +e -g(x ) )dx=c
-e -ƒ(1) +e g(1) =-e -ƒ(2)+ e -g(2)
-1e+e-g(1)=-e-f(2)+1e
e-f(2)+e-g(1)=2ee-f(2)<2e and <2e

 –ƒ(2) < ln2 – 1 and –g(1) < ln2 – 1
ƒ(2) > 1– ln2 and g(1) > 1 – ln2

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