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第74页

信息发布者：

$x^{2}-x - 12$

$x^{2}+7x + 12$

$x^{2}+x - 12$

$x^{2}-7x + 12$

$2x^{2}-13x - 7$

$6x^{2}+7x - 3$

$6x^{3}-5x^{2}-4x$

 解：$\begin{aligned}(-x + 4y)(x - 3y)&=-x\times x+(-x)\times(-3y)+4y\times x+4y\times(-3y)\\&=-x^{2}+3xy + 4xy-12y^{2}\\&=-x^{2}+7xy - 12y^{2}\end{aligned}$

 解：$\begin{aligned}(x + 5y)(x - 5y)&=x^{2}-(5y)^{2}\\&=x^{2}-25y^{2}\end{aligned}$

 解：$\begin{aligned}(3x^{2}-2)(x + 1)&=3x^{2}\times x+3x^{2}\times1-2\times x-2\times1\\&=3x^{3}+3x^{2}-2x - 2\end{aligned}$

 解：$\begin{aligned}&(2x^{2}-3x + 1)(x - 6)\\=&2x^{2}\times x-2x^{2}\times6-3x\times x+3x\times6 + 1\times x-1\times6\\=&2x^{3}-12x^{2}-3x^{2}+18x + x-6\\=&2x^{3}-15x^{2}+19x - 6\end{aligned}$

 解：原方程可化为$6x^{2}-2x - 9x + 3 = 6x^{2}-5x - 12x + 10 + 5.$

 整理，得$6x = 12，$解得$x = 2.$

$-x^{2}-6x + 2$

$-14$