sin^2(160)+cos^2(310)+sin(160)*cos(310) 怎么算?

问题描述:

sin^2(160)+cos^2(310)+sin(160)*cos(310) 怎么算?

(常规方法我不会,不过感觉这一类题好像都这样做)由余弦定理:cosC=(a²+b²-c²)/2ab 和正弦定理:a/sinA=b/sinB=c/sinC得sin²A+sin²B-sin²C=2sinAsinBcosC.即sin²C=sin²A+sin...