-7x(x-7)=56

Solution for -7x(x-7)=56 equation:

-7x(x-7)=56

We move all terms to the left:

-7x(x-7)-(56)=0

We multiply parentheses

-7x^2+49x-56=0

a = -7; b = 49; c = -56;
Δ = b2-4ac
Δ = 492-4·(-7)·(-56)
Δ = 833
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{833}=\sqrt{49*17}=\sqrt{49}*\sqrt{17}=7\sqrt{17}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(49)-7\sqrt{17}}{2*-7}=\frac{-49-7\sqrt{17}}{-14}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(49)+7\sqrt{17}}{2*-7}=\frac{-49+7\sqrt{17}}{-14}
$