-28x=2x^2-90

Solution for -28x=2x^2-90 equation:

-28x=2x^2-90

We move all terms to the left:

-28x-(2x^2-90)=0

We get rid of parentheses

-2x^2-28x+90=0

a = -2; b = -28; c = +90;
Δ = b2-4ac
Δ = -282-4·(-2)·90
Δ = 1504
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:

$\sqrt{\Delta}=\sqrt{1504}=\sqrt{16*94}=\sqrt{16}*\sqrt{94}=4\sqrt{94}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-28)-4\sqrt{94}}{2*-2}=\frac{28-4\sqrt{94}}{-4}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-28)+4\sqrt{94}}{2*-2}=\frac{28+4\sqrt{94}}{-4}
$