8sin^2[A/2]-2cos2A=7 8(1-cosA/2)-2cos2A=7 这步怎样来的?

来源：学生作业学帮网编辑：学帮网时间：2024/06/16 18:39:50

cosA
=cos2(A/2)
=cosA/2 cosA/2 - sinA/2 sinA/2
=cos^2[A/2]-sin^2[A/2]
=cos^2[A/2]+sin^2[A/2]-2sin^2[A/2]
=1-2sin^2[A/2]
所以
2sin^2[A/2] = 1-cosA

化简；1+cos2a+sin^2a= 1+cos2a+sin平方a=2 求证：cos^8A-sin^8A=cos2A(1-1/2sin^2A) 8sin^2(B+C)/2-2cos2A=7 求角A 8sin^2(B+C)/2-2cos2A=7 求角A cos2a等不等于2sin^2a? Sin(π+2a)/(1+cos2a) 化简. cos2a=1-2sin²a 为什么又等于cos2a=-√[1-(sin2a)^2] 求证：1+cos2a+2sin^2a=2 求证 1+2sin^2a-cos2a=2 求证1+cos2a+2sin^a=2 cos2a=√1-sin^2 2a吗已知cos2a=1/4,则sin^2 a=? 已知cos2a=1/4,则sin^2 a= cos2a=1-2sin平方a怎么等于啊证明1-cos2a=2sin平方a cos2a=--√1--sin²2a吗? sin平方a=1-cos2a/2怎么来的