cosC
=(a^2+b^2-c^2)/2ab
=ab/2ab
=1/2
C=60度^这是什么意思啊？余弦定理中c^2=a^2+b^2-2abcosC2abcosC=a^2+b^2-c^2cosC=(a^2+b^2-c^2)/2ab=ab/2ab=1/2C=60度怎样化简得这个啊ab/2ab分子分母同时除以ab