例题:已知9-6y-4y^2=7,求2y^2+3y+7的值.由9-6y-4y^2=7,得-6-4y^2=7-9,即6y+4y^2=2因此,2y^2+3y=1,所以,2y^2+3y+7=8.已知14x+5-21x^2的值是-2,求6x^2-4x+5的值.

问题描述:

例题:已知9-6y-4y^2=7,求2y^2+3y+7的值.
由9-6y-4y^2=7,得-6-4y^2=7-9,即6y+4y^2=2
因此,2y^2+3y=1,所以,2y^2+3y+7=8.
已知14x+5-21x^2的值是-2,求6x^2-4x+5的值.

由14X+5-21X^2=-2,得14X-21X^2=-7
2X-3X^2=-1
3X^2-2X=1
6X^2-4X=2
所以,6X^2-4X+5=7