(1)用配方法证明:-2x²+8x-12必小于0
问题描述:
(1)用配方法证明:-2x²+8x-12必小于0
(2)9x²+y²+24x-6y+25=0,求x+y.
(3)a²+b²+4a-b+17/4=0,求a+b
答
解
-2x²+8x-12
=-2(x²-4x)-12
=-2(x²-4x+4)+8-12
=-2(x-2)²-4
≤-4