cos(2x+60`)cos(x-30`)+sin(2x+60`)sin(x-30`)=1/2求这题的题解...60` 是60度.

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cos(2x+60`)cos(x-30`)+sin(2x+60`)sin(x-30`)=1/2求这题的题解...60` 是60度.
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cos(2x+60`)cos(x-30`)+sin(2x+60`)sin(x-30`)=1/2求这题的题解...60` 是60度.
cos(2x+60`)cos(x-30`)+sin(2x+60`)sin(x-30`)=1/2
求这题的题解...
60` 是60度.

cos(2x+60`)cos(x-30`)+sin(2x+60`)sin(x-30`)=1/2求这题的题解...60` 是60度.
原式=
cos[(2x+60)-（x-30）]=1/2
cos（x+90）=1/2
x+90=±30+2k∏

cos(2x+60-(x-30))=cos(x+90)=1/2
x+90=k*360±60
x=k*360-90±60

逆用余弦公式

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