赞 shirley0754 幼苗
共回答了20个问题采纳率：90% 举报
a^2-b^2-c^2-2ab
=(a^2+b^2-c^2)-2b^2-2ab
=2ab*[(a^2+b^2-c^2)/2ab -2b^2/2ab -1]
=2ab*(cosC -b/a -1)
=2ab*[(cosC-1)-b/a]
因为cosC-1
=(a^2+b^2-c^2)-2b^2-2ab
=2ab*[(a^2+b^2-c^2)/2ab -2b^2/2ab -1]
=2ab*(cosC -b/a -1)
=2ab*[(cosC-1)-b/a]
因为cosC-1
1年前
8
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