990=x^2+2.5x-26

Solution for 990=x^2+2.5x-26 equation:

990=x^2+2.5x-26

We move all terms to the left:

990-(x^2+2.5x-26)=0

We get rid of parentheses

-x^2-2.5x+26+990=0

We add all the numbers together, and all the variables

-1x^2-2.5x+1016=0

a = -1; b = -2.5; c = +1016;
Δ = b2-4ac
Δ = -2.52-4·(-1)·1016
Δ = 4070.25
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-2.5)-\sqrt{4070.25}}{2*-1}=\frac{2.5-\sqrt{4070.25}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2.5)+\sqrt{4070.25}}{2*-1}=\frac{2.5+\sqrt{4070.25}}{-2}
$