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4.9-1/化简:[cos(a+15度)]^2+[sin(a-15度)]^2+[sin(a+180度)]*[cos(a-180度)].
做出来都是1+sin(2a)
人气:394 ℃ 时间:2020-05-10 16:46:58
解答
[cos(a+15度)]^2+[sin(a-15度)]^2+[sin(a+180度)]*[cos(a-180度)]=[cos(2a+30)+1]/2+[1-cos(2a-30)]/2+1/2sin2a=1+[cos(2a+30)-cos(2a-30)]/2+1/2sin2a=1-2sin2a*sin30/2+1/2sin2a=1
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