1. SOLVE IT FOR 0<=X<=兀
sin2x+sin3x=0
2. find cos3θ IN TERMS OF cosθ
TRIGONOMETRY
2011-03-17 4:06 am
回答 (1)
2011-03-17 4:16 am
✔ 最佳答案
sin2x + sin3x = 02sin(5x/2) cos(x/2) = 0sin(5x/2) = 0 or cos(x/2) = 05x/2 = 0, 180, 360,
x/2 = 90,
So, x = 0,72,144,180,
2 cos3θ
= cos(2θ + θ)
= cos2θcosθ - sin2θsinθ
= cosθ(2cos^2θ - 1) - 2sinθ^2 cosθ
= cosθ(2cos^2θ - 1) - 2(1 - cosθ^2) cosθ
= 4cos^3θ - 3cosθ
收錄日期: 2021-04-26 14:54:53
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20110316000051KK00995