由余弦定理得：a^2=b^2+c^2-2bccosA=7^2 b^2+c^2+bc=49 ---(1) (cosA=cos120°=-1/2)b+c=8(b+c)^2=64b^2+c^2+2bc=64 ---(2)(2)-(1):bc=15 ---(3)b(8-b)=158b-b^2=15b^2-8b+15=0(b-3)(b-5)=0b1=3,b2=5.∴c1=8-b1=5c2=...