Question

在△abc中,sinb=sinc,cos2a+3cosa+3cos(b-c)=1

在三角形ABC中,2sin ⒉A=3sin ⒉B+3sin ⒉C,cos2A+3cosA+3cos(B-C)=1 求三角形ABC的三边之比如题

Answer 1

2sin`(`代表平方）A=3sin`B+3sin`C 2a`-3b`=3c` 3cosA+3cos(B-C)=1 cosA=-cos(B+C) 3[-cos(B+C)-cos(B-C)]=1 3sinBsinC=sin`A 3bc=a` 总上｛a=根号3b b=c a:b:c=根号3:1:1