From Förberedande kurs i matematik 1
We rewrite tanv on the left-hand side as sinvcosv, so that
If we then use the Pythagorean identity
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.
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