(x+5)(x+3)=99

Solution for (x+5)(x+3)=99 equation:

(x+5)(x+3)=99

We move all terms to the left:

(x+5)(x+3)-(99)=0

We multiply parentheses ..

(+x^2+3x+5x+15)-99=0

We get rid of parentheses

x^2+3x+5x+15-99=0

We add all the numbers together, and all the variables

x^2+8x-84=0

a = 1; b = 8; c = -84;
Δ = b2-4ac
Δ = 82-4·1·(-84)
Δ = 400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{400}=20$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(8)-20}{2*1}=\frac{-28}{2}
=-14
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(8)+20}{2*1}=\frac{12}{2}
=6
$