3sinb 7sinc

sinB=b/a ·sinA sinC=c/a ·sinA 化简得 3sinB^2+3sinC^2+3sinA^2=2sinBsinC 3﹙b²/a²﹚sin²A+3﹙c²/a²﹚sin²A...

sinB=b/(2R),sinC=c/(2R) sin²A+sin²B+sin²C=2√3 sinAsinBsinC [a/(2R)]^2+[b/(2R)]^2+[c/(2R)]^2=2√3a/(2R)*b/(...

很清楚，这式子要取最小值，必有cosA<0,于是cosA(3sinB+4sinC)=cosA(3sinB+4sin(A+B))=cosA((...

三角函数中的难题?在三角形ABC中，求cosA(3sinB+4sinC)最小值？129 赞同 · 19 评论回答

sinC=sin(π-A-B)=sin(A+B)=sinAcosB+cosAsinB =sinA√(1-sin^2B)+sinB√(1-sin^2A)二倍角公式的运用二倍角公式通过角α的三角...

当三角形的三个内角均为60度时,它们的正弦函数之积最大.即,sin60*sin60*sin60=3^(1/2)/2*3^(1/2)/2*3^(1/2=(3/8)*3^(1/2)

成等比数列.根据正弦定理:a/sinA=b/sinB=c/sinC=2R则有:a=2RsinA,b=2RsinB,c=2RsinC因为a,b,c成等比数列,即:b^2=ac所以:(2RsinB)^2=(2RsinA)(2RsinC...

在三角形ABC中，sinA=sinBsinC，求CosA最小值？由1cos2A=sinBsinC≤(sinB+sinC2)2≤sin2B+C2=cos2A2=...

1、A=60度,则:B+C=120°所以:B=120°-C代入sinB=3sinCsin(120°-C)=3sinC(√3/2)cosC+(1/2)sinC=3sinC即:(√3/2)cosC=(5/2)sinC所以:tanC=sinC/cosC...