can anyone help me with this...
i have to prove that the left side = the right side...
sin^4A - cos^4A = 2sin^2A -1
thanks~
trigonometric functions (prove equalities)?
2008-08-25 4:41 pm
回答 (1)
2008-08-25 4:48 pm
✔ 最佳答案
[sin^2A]^2 - [cos^2A]^2 = 2sin^2A -1LHS > using X^2 - Y^2 = (X+Y) (X-Y)
[sin^2A + cos^2 A][sin^2 A - cos^2A]
[1] [sin^2 A - (1- sin^2 A)]
= 2 sin^2 A - 1 = RHS
收錄日期: 2021-05-03 01:51:51
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20080825084125AAsNZGB