Let be a non-zero real number. Suppose f: R R is a differentiable function such that f(0)=2 and x - f(x)=1. If f (x)= f(x)+3, for all x R, then f (- e 2 ) is equal to :
- 7
- 9
- 3
- 5
Answer
BONUS
Solution
f'(x)- f(x)=3 (linear), I.F. =e- x
f(x)=- 3 +c e x, and f(0)=2 c=2+ 3
>0: e x 0 as x - - 3 =1 =-3, contradicting >0
<0: e x a finite limit needs c=0 f f(0)=2, but the limit is 1: contradiction
no satisfies all the conditions, the data are inconsistent question dropped
Answer: Bonus (full marks to all who attempted)