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1+cos2α,cos2α+cos2β

怎么推导 sin^2α=(1-cos2α)/2 cos^2α=(1 cos2α)/2? 急求!
怎么推导 sin^2α=(1-cos2α)/2 cos^2α=(1 cos2α)/2? 急求!已知sin(π/6-α)=1/3,求cos(2/3π 2α)
已知sin(π/6-α)=1/3,求cos(2/3π 2α)又0. 2013-11-25 sinα=
又0. 2013-11-25 sinα=已知(sinα cosα)/(sinα-cosα)=2,求下列各式的值 (1)(3sinα cos
已知(sinα cosα)/(sinα-cosα)=2,求下列各式的值 (1)(3sinα coscosx为什么等于1/2(1 cos2x)
cosx为什么等于1/2(1 cos2x)
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