sinB*sinC=cos^2(A/2)cos^2(A/2)=cos^2[π/2 - (B+C)/2]=sin^2[(B+C)/2]=[1-cos(B+C)]/2sinB*sinC=cos^2(A/2)=[1-cos(B+C)]/2sinBsinC=1/2 - (cosBcosC - sinBsinC)/2cosBcosC + sinBsinC = 1cos(B-C)=1由于是在△AB...这速度= = 哥！