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x²;-4x+27=(x-2)²;+23因(x-2)²;≥0所以x²;-4x+27>0-6x²;+24x-25=-6(x²;-4x)-25=-6(x-2)²;-25+24=-6(x-2)²;-1因-6(x-2)²;≤0所以-6x²;+24x-25<0
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