cos(a+π/)=-1/3 a∈(0,π/2) 求coSa
问题描述:
cos(a+π/)=-1/3 a∈(0,π/2) 求coSa
答
cos(a+π/2)=-1/3
cosacosπ/2-sinasinπ/2=-1/3
-sina=-1/3
sina=1/3
∵a∈(0,π/2)
∴cos²a =1-sin²a
=2根号2/3