0=(x+15)(x-13)

Solution for 0=(x+15)(x-13) equation:

0=(x+15)(x-13)

We move all terms to the left:

0-((x+15)(x-13))=0

We add all the numbers together, and all the variables

-((x+15)(x-13))=0

We multiply parentheses ..

-((+x^2-13x+15x-195))=0


We calculate terms in parentheses: -((+x^2-13x+15x-195)), so:

(+x^2-13x+15x-195)

We get rid of parentheses

x^2-13x+15x-195

We add all the numbers together, and all the variables

x^2+2x-195

Back to the equation:

-(x^2+2x-195)


We get rid of parentheses

-x^2-2x+195=0

We add all the numbers together, and all the variables

-1x^2-2x+195=0

a = -1; b = -2; c = +195;
Δ = b2-4ac
Δ = -22-4·(-1)·195
Δ = 784
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{784}=28$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-2)-28}{2*-1}=\frac{-26}{-2}
=+13
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2)+28}{2*-1}=\frac{30}{-2}
=-15
$