(a+3)(a-2) 与(a+1/2)2比大小

(a+3)(a-2)-(a+1/2)×2
=a²+a-6-2a-1
=a²-a-7
=(a-½)²-（29/4）≥ 0
解得：
a≥±√29/2+1/2
即：
a≥√29/2+1/2,或a≤-√29/2+1/2时,
(a+3)(a-2)比(a+1/2)2大.