For the function f(x)=e |x|-|x|, x R, consider the following statements : In the light of the above statements, choose the correct answer from the options given below :
- Both Statement I and Statement II are true
- Both Statement I and Statement II are false
- Statement I is true but Statement II is false
- Statement I is false but Statement II is true
Answer
(1) Both Statement I and Statement II are true
Solution
For x 0: f(x)=e x-x f'(x)= x e x-1
For x<0: |x|=- x, |x|=-x f(x)=e- x+x f'(x)=1- x e- x
Both pieces are differentiable, so only x=0 needs checking:
f'(0+)=1 e0-1=0, f'(0-)=1-1 e0=0
f'(0+)=f'(0-)=0 (the corners of e |x| and -|x| at 0 cancel)
f is differentiable for all x Statement I is true
For x (- , - 2 ): x<0 and e- x>0
f'(x)=1- x e- x>1>0
f is increasing in (- , - 2 ) Statement II is true
Answer: (1)