(x+10)(x+5)=300

Solution for (x+10)(x+5)=300 equation:

(x+10)(x+5)=300

We move all terms to the left:

(x+10)(x+5)-(300)=0

We multiply parentheses ..

(+x^2+5x+10x+50)-300=0

We get rid of parentheses

x^2+5x+10x+50-300=0

We add all the numbers together, and all the variables

x^2+15x-250=0

a = 1; b = 15; c = -250;
Δ = b2-4ac
Δ = 152-4·1·(-250)
Δ = 1225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1225}=35$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(15)-35}{2*1}=\frac{-50}{2}
=-25
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(15)+35}{2*1}=\frac{20}{2}
=10
$