sin(a/2)=1/3
sin^2(a/2)=1/9,
(cosa/2)^2=8/9
cos(a/2)=2√2/3
sina=2*1/3*2√2/3=4√2/9
cosa=7/9
tana=4√2/7
斜率K=tana=4√2/7
直线方程y=4√2x/7+2.
sin(a/2)=1/3
sin^2(a/2)=1/9,
(cosa/2)^2=8/9
cos(a/2)=2√2/3
sina=2*1/3*2√2/3=4√2/9
cosa=7/9
tana=4√2/7
斜率K=tana=4√2/7
直线方程y=4√2x/7+2.