cos2A=6cos2C-5 cos2A=-1/3 c=根号3 求a

日期：2021-07-04 18:26:24 人气：1

cos2A=6cos2C-5
1-2sin²A=6(1-2sin²C)-5
sin²A=6sin²C
sinA>0，sinC>0
sinA=√6sinC
由正弦定理得a/c=sinA/sinC
a=csinA/sinC=√3?√6sinC/sinC=3√2
a为3√2