先化简,再求值:已知x²+x=12,求(x-2)(2x-3)-(x-4)²-14的值

先化简,再求值:已知x²+x=12,求(x-2)(2x-3)-(x-4)²-14的值
先化简,再求值:已知x²+x=12,求(x-2)(2x-3)-(x-4)²-14的值

先化简,再求值:已知x²+x=12,求(x-2)(2x-3)-(x-4)²-14的值
(x-2)(2x-3)-(x-4)²-14
=2x^2-4x-3x+6-x^2+8x-16-14
=x^2+x-24
=12-24
=-12

(x-2)(2x-3)-(x-4)²-14
=2x²-7x+6-x²+8x-16-14
=x²+x-24
=12-24
=-12

(x-2)(2x-3)-(x-4)²-14
=2x²-7x+6-(x²-8x+16)-14
=2x²-7x+6-x²+8x-16-14
=x²+x-24
已知x²+x=12
∴x²+x-24
=12-24
=-12