现在就
要
y=根号3sinA/(1+3sin^2A)=根号3/(1/sinA+3sinA)
A属于(0,派),0<sinA<=1
1/sinA+3sinA>=2根号3,当1/sinA=3sinA时最小,sinA=根号3/3
当sinA趋向于0时,趋向于无穷大,所以1/sinA+3sinA的值域是[2根号3,无穷大)
0<根号3/(1/sinA+3sinA)<=1/2