-700=x^2-140x

Solution for -700=x^2-140x equation:

-700=x^2-140x

We move all terms to the left:

-700-(x^2-140x)=0

We get rid of parentheses

-x^2+140x-700=0

We add all the numbers together, and all the variables

-1x^2+140x-700=0

a = -1; b = 140; c = -700;
Δ = b2-4ac
Δ = 1402-4·(-1)·(-700)
Δ = 16800
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:

$\sqrt{\Delta}=\sqrt{16800}=\sqrt{400*42}=\sqrt{400}*\sqrt{42}=20\sqrt{42}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(140)-20\sqrt{42}}{2*-1}=\frac{-140-20\sqrt{42}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(140)+20\sqrt{42}}{2*-1}=\frac{-140+20\sqrt{42}}{-2}
$