在三角形ABC中,m=(cosC/2 ,sinc/2 ),n=(cosc/2 ,-sin c/2),且 mn的夹角为 3/π

m.n=|m|*|n|cos(π/3)=cos(π/3)=1/2cos^2(C/2)-sin^2(C/2)=1/2 cosC=1/2所以 C=π/32.设AB=c=7/2,AC=b,BC=a (absinC)/2=3√3/2 absin(π/3)=3√3ab=6(1) c^2=a^2+b^2-2abcosC=a^2+b^2-ab (a+b)^2=c...