已知锐角（a+π/3)的终边经过点P（1,4×3＾1／2）,则cosa＝?
问题描述：
已知锐角（a+π/3)的终边经过点P（1,4×3＾1／2）,则cosa＝?
答
r^2=2=1+48=49
r=7
cos（a+π/3)=1/7
sin（a+π/3)=4√3/7
cosa=cos（a+π/3-π/3)
=cos（a+π/3)cosπ/3+sin（a+π/3)sinπ/3
=1/7*1/2+4√3/7*√3/2
=1/14+12/14
=13/14