正弦定理:a/sinA=b/sinB=c/sinC=常数1/sinA=√2/sin45oA=30o或A=150o(舍去)故A=30o
正弦定理a/sinA=b/sinB
根据正弦定理a/sinA=b/sinB1/sinA=√2/sin45sinA=1/2A=30度