Question

For which value of 0 is sin 0=-1? (See attached image for clearer question)

Answer 1

The sine of theta is equal to -1 when the end point of the blue radius in the image has a y-coordinate equal to -1.

The only angle between 0 and 2*pi where the sine is equal to -1 is when theta = 3pi/2:

Therefore the answer is 3pi/2.