SOLUTION: please prove that: sin^4 theta - cos^4 theta = 2sin^2 theta - 1.

Algebra ->  Trigonometry-basics -> SOLUTION: please prove that: sin^4 theta - cos^4 theta = 2sin^2 theta - 1.      Log On


   

Question 767174: please prove that: sin^4 theta - cos^4 theta = 2sin^2 theta - 1.
Answer by Edwin McCravy(20060) About Me  (Show Source):
You can put this solution on YOUR website!
 
sin4(q) - cos4(q) = 2sin2(q) - 1

[sin2(q) - cos2(q)][sin2(q) + cos2(q)]

[sin2(q) - cos2(q)][1]

sin2(q) - cos2(q)

sin2(q) - [1 - sin2(q)]

sin2(q) - 1 + sin2(q)

2sin2(q) - 1

Edwin