sinA+sinB-sinC=4sin(A/2)sin(B/2)cos(C/2)
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sinA+sinB-sinC=4sin(A/2)sin(B/2)cos(C/2)
证明上式
证明上式
![sinA+sinB-sinC=4sin(A/2)sin(B/2)cos(C/2)](/uploads/image/z/17004344-32-4.jpg?t=sinA%2BsinB-sinC%3D4sin%28A%2F2%29sin%28B%2F2%29cos%28C%2F2%29)
右边=4sinA/2sinB/2sinA+B/2=4sinA/2sinB/2[sinA/2cosB/2+sinB/2cosA/2]=4(sinA/2)^2sinB/2cosB/2+4(sinB/2)^2sinA/2cosA/2=2(sinA/2)^2sinB+2(sinB/2)^2sinA=sB(1-sA)+sA(1-sB)=sA+sB-sAcB-sBcA=sA+sB-s(A+B)=sA+sB-sC
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cos^2A - cos^2B + sin^2C=2cosA *sinB *sinC
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