1mn=0得a2+b2-c2=ab,cosc=(a2+b2-c2)\2ab=1\2
c=60°
2 sina+sinb=sin(180°-c-b)+sinb=sin(陵嫌120°-b)+sinb
展开化简再提取根号3得尺辩手=根号灶掘3sin(b+30°)
(b大于0小于120°)
则范围大于2分之根号三小于根号3
由m*n=0知a*a-c*c+b*b-a*b=0得a*a+b*b-c*c=a*b
cosC=(a*a+b*b-c*c)/2a*b=a*b/搜没2a*b=1/塌启2
所以C=60°。团漏如
sinA+sinB=