ace4587
幼苗
共回答了13个问题采纳率:92.3% 举报
(1)cos²A-cos²B=√3sinAcosA-√3sinBcosB,
1/2cos2A-1/2cos2B=√3/2sin2A-√3/2sin2B,
sin(2A-π/6)=sin(2B-π/6),
a≠b,则2A-π/6=π-2B+π/6,
A+B=2π/3,
C=π/2
(2)a/sinA=c/sinC,
a=8/5,
因为a<c,则0<A<π/3,则cosA=3/5,
sinB=sin(A+C)=(4+3√3)/10,
S=1/2*(4+3√3)/10*(8/5)*√3=(4√3+9)/25
1年前
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