90=9x^2+10x

Solution for 90=9x^2+10x equation:

90=9x^2+10x

We move all terms to the left:

90-(9x^2+10x)=0

We get rid of parentheses

-9x^2-10x+90=0

a = -9; b = -10; c = +90;
Δ = b2-4ac
Δ = -102-4·(-9)·90
Δ = 3340
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:

$\sqrt{\Delta}=\sqrt{3340}=\sqrt{4*835}=\sqrt{4}*\sqrt{835}=2\sqrt{835}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-10)-2\sqrt{835}}{2*-9}=\frac{10-2\sqrt{835}}{-18}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-10)+2\sqrt{835}}{2*-9}=\frac{10+2\sqrt{835}}{-18}
$