Trig. Identity
回答 (1)
2011-11-01 4:54 am
✔ 最佳答案
cos⁴x= (cos² x)² = ( (cos 2x + 1)/2 )² = (cos² 2x + 2 cos 2x + 1) / 4 = ((cos 4x + 1)/2 + 2 cos 2x + 1) / 4 = ( cos 4x + 1 + 4 cos 2x + 2 ) / 8= (4 cos 2x + cos 4x + 3) / 8True.
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