The sine function goes from -1, then to 0, then to 1, and back again. The max an mins are -1 and 1, sine function has a zero value each time it hits 180 or a multiple of 180: 0, 180, 360, etc
That is easy to see if you use a rectangle triangle, its definition is: sine a is equal to the division of the opossite cathetus over the hypothenuse, thus, for that division to be zero, the opposite cathetus has to be zero, that is when the angle is 0, or 180, 360, etc
