Consider the function
f(x)=⎩⎨⎧sinx,x2,4,x≤00<x<2x≥2.
Which of the following gives f′(x) for all real numbers x?
a) f′(x)=sinx for x<0, 2x for 0<x<2, and 0 for x>2
b) f′(x)=cosx for x<0, 2x for 0<x<2, and 0 for x>2
c) f′(x)=cosx for x<0, 2x for 0≤x≤2, and 0 for x>2
d) f′(x)=cosx for x<0, 2x for 0<x<2, and 4 for x>2