tsunt
春芽
共回答了12个问题采纳率：83.3% 举报
因A+B+C=π,又A+C=2B
得B=π/3
1/cosA+1/cosC=-2√2
=>(cosA+cosC)=-2√2cosAcosC
=>2cos(A-C)/2cos(A+C)/2=-√2[cos(A+C)+cos(A-C)]
=>cos(A-C)/2=-√2[-1/2+cos(A-C)]
=>cos(A-C)/2=-√2[-1/2+2cos²(A-C)/2-1]
=>4cos²(A-C)/2+√2cos(A-C)/2-3=0(|A-C|/2
1年前
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