已知方程组｛2x+y=2a,x+2y=1-5a｝,若x+y的值为非负数,求a的取值范围.急用,

题目

已知方程组｛2x+y=2a,x+2y=1-5a｝,若x+y的值为非负数,求a的取值范围.急用,
急急急····························

答案

两式相加,3x+3y=1-3a,(1/3)×（1 - 3a）=(x+y)≥0,(1/3-a)≥0 ,a≤（1/3)