900=y^2+10y

Solution for 900=y^2+10y equation:

900=y^2+10y

We move all terms to the left:

900-(y^2+10y)=0

We get rid of parentheses

-y^2-10y+900=0

We add all the numbers together, and all the variables

-1y^2-10y+900=0

a = -1; b = -10; c = +900;
Δ = b2-4ac
Δ = -102-4·(-1)·900
Δ = 3700
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{3700}=\sqrt{100*37}=\sqrt{100}*\sqrt{37}=10\sqrt{37}$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-10)-10\sqrt{37}}{2*-1}=\frac{10-10\sqrt{37}}{-2}
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-10)+10\sqrt{37}}{2*-1}=\frac{10+10\sqrt{37}}{-2}
$