Question

2sinx / cos3x = tan3x - tanx -verify the identity-

Answer 1

cos3x+tan3x=0

⟹cos3x=−tan3x

⟹cos3x=−sin3xcos3x

⟹cos23x=−sin3x

⟹1−sin23x=−sin3x

⟹sin23x−sin3x−1=0

This is a quadratic equation in sin3x.

sin3x=−(−1)±(−1)2−4×1×(−1)−−−−−−−−−−−−−−−−−√2×1

sin3x=1±5–√2

If x takes real values, the upper sign must be rejected.

sin3x=1−5–√2

⟹3x=nπ+(−1)nsin−11−5–√2

⟹x=13[nπ+(−1)nsin−11−5–√2]

Explanation:

Hope this kind of helps