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)

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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)].
• 化简：[cos(a+15度)]^2+[sin(a-15度)]^2+[sin(a+180度)]*[cos(a-180度)].
• 化简：[cos(a+15度)]^2+[sin(a-15度)]^2+[sin(a+180度)]*[cos(a-180度)].请大家解释一下.[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 第一步有点看不懂 用的是什么公式啊
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• 化简：[cos(a+15度)]^2+[sin(a-15度)]^2+[sin(a+180度)]*[cos(a-180度)].请大家解释一下.[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 第一步有点看不懂 用的是什么公式啊
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