gggixc
幼苗
共回答了15个问题采纳率:86.7% 举报
cosa=cos((a/2+b/2)+(a/2-b/2))
cosb=cos(-b)=cos((a/2-b/2)-(a/2+b/2))
cos((a/2+b/2)+(a/2-b/2))=
cos(a/2+b/2)*cos(a/2-b/2)-sin(a/2+b/2)*sin(a/2-b/2)
cos((a/2-b/2)-(a/2+b/2))=
cos(a/2+b/2)*cos(a/2-b/2)+sin(a/2+b/2)*sin(a/2-b/2)
两式相加即可得到你要证的公式
cos(a)+cos(b)=2cos(a/2+b/2)cos(a/2-b/2)
1年前
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