The values of sin cycle on the domain 0 to 2π
The value of sin(π/2) = 1
The value of sin(2π/2) = 0
The value of sin(3π/2) = sin(π + π/2)= -1
Therefore, if the angle can be written as:
nπ + π/2, where n is any odd number, the value of sin(nπ + π/2) = -1
sin(11π/2) = sin(5π + π/2) = -1