Problem - 3616
Solve this equation $(x-2)(x+1)(x+4)(x+7)=19$.
Note that $(x-2)(x+7)=x^2 + 5x - 14$ and $(x+1)(x+4)=x^2+5x+4$ only differ in constant terms. Let
$$y=\frac{(x-2)(x+7) + (x+1)(x+4)}{2}= x^2 + 5x -5$$
Then
\begin{align}
(x-2)(x+1)(x+4)(x+7)&=19\\
\Big((x-2)(x+7)\Big)\Big((x+1)(x+4)\Big)&=19\\
(y-9)(y+9)&=19\\
y_{1,2}&=\pm 10
\end{align}
When $y=10$, $x^2-5x-5=10 \implies x_{1,2}=\boxed{\frac{-5\pm\sqrt{85}}{2}}$.
When $y=-10$, $x^2-5x-5=-10 \implies x_{3,4}=\boxed{\frac{-5\pm\sqrt{5}}{2}}$.