From Förberedande kurs i matematik 1
We rewrite
tan v
on the left-hand side as
sinvcosv, so that
tan2v=sin2vcos2v
If we then use the Pythagorean identity
cos2v+sin2v=1
and rewrite
cos2v
in the denominator as
1−sin2v , we get what we are looking for on the right-hand side. The whole calculation is
tan2v=sin2vcos2v=sin2v1−sin2v
