先化简,在求值:(1)已知x^2-5x=14,求(x-1)(2x-1)-(x+1)^2+1的值

问题描述:

先化简,在求值:(1)已知x^2-5x=14,求(x-1)(2x-1)-(x+1)^2+1的值

x^2-5x-14=0
x^2-5x=14
(x-1)(2x-1)-(x+1)²+1
=2x²-3x+1-x²-2x-1+1
=x²-5x+1
=14+1
=15

x^2-5x-14=0
(x+2)(x-7)=0 x1=-2,x2=7
(x-1)(2x-1)-(x+1)^2+1
=2x^2-3x+1-x^2-2x-1+1
=x^2-5x+1
x1=-2, 原式=4-20+1=-15
x2=7,原式=49-35+1=15