From Förberedande kurs i matematik 1
A useful technique for calculating the value of a trigonometric function for angles that don't lie between
0
and
2
is to use the unit circle. If we draw a line which starts at the origin and makes a certain angle relative to the positive part of the
x
-axis, we can see that the cosine of that angle is the
x
-coordinate of the point of intersection between the line and the unit circle. In the same way, the sine of the angle is the
y
-coordinate of the intersection point.
In this case, we see immediately that
sin
−2
= −1 .
