赞 hkwCrystal 幼苗
共回答了20个问题采纳率：85% 举报
B+C=π-A
sin^2(B+C)/2+cos2A
=sin^2[π/2-A/2]+cos2A
=cos^2(A/2)+cos2A
=(1+cosA)/2+2cos^2A-1 cosA=4/5
=(1+4/5)/2+32/25-1
=9/10+7/25
=59/50
sin^2(B+C)/2+cos2A
=sin^2[π/2-A/2]+cos2A
=cos^2(A/2)+cos2A
=(1+cosA)/2+2cos^2A-1 cosA=4/5
=(1+4/5)/2+32/25-1
=9/10+7/25
=59/50
1年前
8
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