有3个网友回答
-2X²-8X+40=0
x²+4x-20=0
x=-6.898989898989
或2.898989898989
-2x^2-8x+40=0,
整理x^2+4x-20=0,
a=1,b=4,c=-20,
判别式△=b^2-4ac=16+4*20=96,
所以x=（-4±√96）/2=(-4±4√6)/2=-2±2√6
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