(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
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![(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](/uploads/image/z/1252975-31-5.jpg?t=%EF%BC%881%EF%BC%89%E7%94%A8%E9%85%8D%E6%96%B9%E6%B3%95%E8%AF%81%E6%98%8E%EF%BC%9A-2x%26%23178%3B%2B8x-12%E5%BF%85%E5%B0%8F%E4%BA%8E0%EF%BC%882%EF%BC%899x%26%23178%3B%2By%26%23178%3B%2B24x-6y%2B25%3D0%2C%E6%B1%82x%2By.%EF%BC%883%EF%BC%89a%26%23178%3B%2Bb%26%23178%3B%2B4a-b%2B17%2F4%3D0%2C%E6%B1%82a%2Bb)
(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
(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
(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
解
-2x²+8x-12
=-2(x²-4x)-12
=-2(x²-4x+4)+8-12
=-2(x-2)²-4
≤-4