tana/2=1/2
sina=2tana/(1+tan^2a)=4/5
cosa=3/5
cos(β-a)=√2/10
sin(β-a)=4√6/10
sinβ=sin(β-a+a)=sin(β-a)cosa+cos(β-a)sina
=4√李嫌6/缓物10*3/5+√哪哪手2/10 *4/5
=2(√6＋√2）/25
已知0<a<π/2<β<π tana/2=1/2 cos(β-a)=根号2/10 求sina和β的值
tana/2=1/2
sina=2tana/(1+tan^2a)=4/5
cosa=3/5
cos(β-a)=√2/10
sin(β-a)=4√6/10
sinβ=sin(β-a+a)=sin(β-a)cosa+cos(β-a)sina
=4√李嫌6/缓物10*3/5+√哪哪手2/10 *4/5
=2(√6＋√2）/25