8sin^2[A/2]-2cos2A=7 8(1-cosA/2)-2cos2A=7 这步怎样来的?
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![8sin^2[A/2]-2cos2A=7 8(1-cosA/2)-2cos2A=7 这步怎样来的?](/uploads/image/z/14186119-31-9.jpg?t=8sin%5E2%5BA%2F2%5D-2cos2A%3D7+8%281-cosA%2F2%29-2cos2A%3D7+%E8%BF%99%E6%AD%A5%E6%80%8E%E6%A0%B7%E6%9D%A5%E7%9A%84%3F)
8sin^2[A/2]-2cos2A=7 8(1-cosA/2)-2cos2A=7 这步怎样来的?
8sin^2[A/2]-2cos2A=7 8(1-cosA/2)-2cos2A=7 这步怎样来的?
8sin^2[A/2]-2cos2A=7 8(1-cosA/2)-2cos2A=7 这步怎样来的?
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
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8sin^2(B+C)/2-2cos2A=7 求角A
8sin^2(B+C)/2-2cos2A=7 求角A
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cos2a=1-2sin²a 为什么又等于cos2a=-√[1-(sin2a)^2]
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cos2a=√1-sin^2 2a吗
已知cos2a=1/4,则sin^2 a=?
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cos2a=--√1--sin²2a吗?
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