.△ABC中,角A,B,C所对的边分别为a,b,c,B=π/3,cosA=4/5,b=√3 (1)sinC值 (2)△面积sinC=sin(120-A)=sin120cosA-cos120sinA=(根下3)/2*(4/5)+(1/2)*(3/5)=(4倍根下3 +3)/10a=b/sinB*sinA=2*3/5=6/5S=0.5absinC=0.5*6/5*(根下3)*(4倍
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![.△ABC中,角A,B,C所对的边分别为a,b,c,B=π/3,cosA=4/5,b=√3 (1)sinC值 (2)△面积sinC=sin(120-A)=sin120cosA-cos120sinA=(根下3)/2*(4/5)+(1/2)*(3/5)=(4倍根下3 +3)/10a=b/sinB*sinA=2*3/5=6/5S=0.5absinC=0.5*6/5*(根下3)*(4倍](/uploads/image/z/2506597-61-7.jpg?t=.%E2%96%B3ABC%E4%B8%AD%2C%E8%A7%92A%2CB%2CC%E6%89%80%E5%AF%B9%E7%9A%84%E8%BE%B9%E5%88%86%E5%88%AB%E4%B8%BAa%2Cb%2Cc%2CB%3D%CF%80%2F3%2CcosA%3D4%2F5%2Cb%3D%E2%88%9A3+%EF%BC%881%EF%BC%89sinC%E5%80%BC+%EF%BC%882%EF%BC%89%E2%96%B3%E9%9D%A2%E7%A7%AFsinC%3Dsin%28120-A%29%3Dsin120cosA-cos120sinA%3D%28%E6%A0%B9%E4%B8%8B3%29%2F2%2A%284%2F5%29%2B%281%2F2%29%2A%283%2F5%29%3D%284%E5%80%8D%E6%A0%B9%E4%B8%8B3+%2B3%29%2F10a%3Db%2FsinB%2AsinA%3D2%2A3%2F5%3D6%2F5S%3D0.5absinC%3D0.5%2A6%2F5%2A%EF%BC%88%E6%A0%B9%E4%B8%8B3%EF%BC%89%2A%284%E5%80%8D)
.△ABC中,角A,B,C所对的边分别为a,b,c,B=π/3,cosA=4/5,b=√3 (1)sinC值 (2)△面积sinC=sin(120-A)=sin120cosA-cos120sinA=(根下3)/2*(4/5)+(1/2)*(3/5)=(4倍根下3 +3)/10a=b/sinB*sinA=2*3/5=6/5S=0.5absinC=0.5*6/5*(根下3)*(4倍
.△ABC中,角A,B,C所对的边分别为a,b,c,B=π/3,cosA=4/5,b=√3 (1)sinC值 (2)△面积
sinC=sin(120-A)=sin120cosA-cos120sinA=(根下3)/2*(4/5)+(1/2)*(3/5)=(4倍根下3 +3)/10
a=b/sinB*sinA=2*3/5=6/5
S=0.5absinC=0.5*6/5*(根下3)*(4倍根下3 +3)
a/sinA=b/sinB ,a=b/sinB*sinA=6/5
S=1/2*absinC=(9根号3+36)/50
.△ABC中,角A,B,C所对的边分别为a,b,c,B=π/3,cosA=4/5,b=√3 (1)sinC值 (2)△面积sinC=sin(120-A)=sin120cosA-cos120sinA=(根下3)/2*(4/5)+(1/2)*(3/5)=(4倍根下3 +3)/10a=b/sinB*sinA=2*3/5=6/5S=0.5absinC=0.5*6/5*(根下3)*(4倍
sinB=√3/2,cosB=1/2
cosA=4/5,sinA=3/5
sinC=sin(180-A-B)=sin(A+B)=sinAcosB+cosAsinB=3/5×1/2+4/5×√3/2=(4√3+3)/10
正弦定理
a/sinA=b/sinB
a/(3/5)=√3/(√3/2)
a=6/5
S=1/2absinC=1/2×6/5×√3×(4√3+3)/10=(9√3+36)/10