Processing Math: Done

From Förberedande kurs i matematik 1

If we write the angle 57 as

57=55+2=+52

we see that 75 is an angle in the third quadrant.

The angle between 0 and which has the same x-coordinate as the angle 75, and hence the same cosine value, is the reflection of the angle 75 in the x-axis, i.e.

v=−52=53.