Question #d800a
1 Answer
Mar 1, 2017
Develop the left side:
LS = cos^4 a - sin^4a = (cos^2 a - sin^2 a)(cos^2 a + sin^2 a)
Because:
(cos^2 a + sin^2 a) = 1, and
(cos^2 a - sin^2 a) = cos 2a (trig identity)
Then:
