Question

which function's graph has a period of 2?
y=2sin3x
y=3cos2x
y=-4sinpix
y=cos(x-pi/2)

Answer 1

period = 2pi / b , where y = a sin (bx + c) + d

Answer 2

so your third choice -4 sin pi * x , the period is 2pi / pi = 2