sinx^2=(1-cos2x)/2是怎么来的。 cos2x=2cosx^2-1怎么来的
\u4e3a\u4ec0\u4e48cos2x=1-2(sinx)^2\u4e3a\u4ec0\u4e48 cos 2x =1-2sin² x ?
\u56e0 \u4e3a cos 2x =cos² x - sin² x = 1 - 2sin² x
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cos2x=cos²x-sin²x
=2cos²x-1
=1-2sin²
\u6269\u5c55\u8d44\u6599\uff1a
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\u4e8c\u500d\u89d2\u516c\u5f0f\uff1a
变形即可
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