k-f=(cosa-cosp,sia-sinp) sia=sin(a-p+p)=sin(a-p)cosp+cos(a-p)sinp
|k-f|^2=(cosa-cosp)^2+(sia-sinp)^2=2-2(cosacosp+siasinp)=2-2cos(a-p)=13/16
cos(a-p)=5/13
0sin(a-p)=12/13
负二岁碰分之乎尘谈π
=12/13*3/5+5/13*(-4)/5=16/65
解法兄伏是对的 公式不一定用的对 忘了好多年了!