求函数值域:
y=2-√(x-x平方)
先求√(x-x平方)的取值范围[0,1/2]
-√(x-x平方)的取值范围是[-1/2,0]
然后+2为[3/2,2]
y=2-√[-(x-1/2)^2+1/4]
因为 0≤-(x-1/2)^2+1/4≤1/4 0≤√[-(x-1/2)^2+1/4]≤1/2
y∈[2/3,2]