In a unit circle, the y co-ordinate is .

If this is positive, then the y co-ordinate is above the x-axis.

If you draw a horizontal line through this y-axis value,

it cuts the circle in two places.

Calculating inverse sine gives you the acute angle the point on the circle makes with the positive x-axis.

As the situation is symmetrical, how do you calculate the answer that

your calculator does not give you?