已知非空集合A={-2≤x ≤a},B={ y|y=2x+3,x∈A},C={ z|z=x^2,x∈A},且C⊆B,求a的取值范围.

A={x| -2≤x≤a},B={y| y=2x+3 ,x∈A}C={z| z=x^2,x∈A}C= {x| 0≤x≤4 or 0≤x≤a^2 }B= { x| -1 ≤x ≤ 2a+3 } C is subset of B,then4≤2a+3 and 2a+3≥a^2 a≥1/2 and a^2-2a-3≤ 0a ≤1/2 and -1≤a≤3=> 1/2≤...