若2x²-5x+ (2x²-5x+1)分之8-5=0,求2x²-5x-1的值

问题描述:

若2x²-5x+ (2x²-5x+1)分之8-5=0,求2x²-5x-1的值

设2x²-5x-1=y
2x²-5x+ (2x²-5x+1)分之8-5=0
2x²-5x+1+ (2x²-5x+1)分之8-6=0
y+(8/y)-6=0
y²+8-6y=0
(y-2)(y-4)=0
y1=2 y2=4
2x²-5x-1=2或
2x²-5x-1=4