=
A point on a circle
A point goes round a circle of radius 1. Its height is sin θ.
The height draws a wave
Lay the angle out along a line, and the height draws a wave.
The lowest point
At what angle is the wave at its lowest?
The bottom of the circle
The wave is lowest where the point is lowest on the circle.
There: 270°, where sin θ is −1.
Right: at 270° the point is at the bottom of the circle, where its height is −1.
Turn your phone sideways