y=(sinx*cosx)/(1+sinx+cosx)的定义域和值域
y = ½ (sin2x)[1-(sinx+cosx)]/{[1+sinx+cosx][1-(sinx+cosx)]}
= ½ (sin2x)[1-(sinx+cosx)]/[1-(sinx+cosx)²]
= ½ (sin2x)[1-(sinx+cosx)]/(-sin2x)
= -[1-(sinx+cosx)]/2
= -1/2 +(sinx+cosx)/2
= -1/2 +[sinx+sin(π/2 - x)]/2
= -1/2 +sin(π/4)cos(π/4 - x)
= -1/2 +[√2)/2]cos(π/4 - x)
-1/2 -√2)/2 ≤ y ≤ -1/2 +√2)/2
-1/2 -√2)/2 ≤ y ≤ -1/2 +√2)/2
所以：
定义域：x ∈R
值 域：-1/2 -√2)/2 ≤ y ≤ -1/2 +√2)/2