Can anyone tell me whether sin|x| and cos|x| is differentiable at x=0 ?
As far as i know, cos(x) and sin(x) is differentiable at all x.
If i try to solve this,
lim h->0 (f(x+h) - f(x))/h
when x=0, and substitute cos|x| for f(x).
lim h->0 (cos|h| - cos|0|)/(h) = 1,
so cos|x| is...