Question

sina乘以sina=sin(30+b)sin(30-b)+sinb乘以sinb 求a的大小

Answer 1

设cosA =b/c,sinB=b/c,cosB=a/c,sinA=a/c(c为斜边)

根据题意知此三角形为等腰直角三角形

即a=b,则cosA=cosB

等式两边可约去cosA和cosB

则有sinB=sinA

整理得：sinA-sinB=0,即·sin(A-B)=0