-28=(x+9)(x-19)

Solution for -28=(x+9)(x-19) equation:

-28=(x+9)(x-19)

We move all terms to the left:

-28-((x+9)(x-19))=0

We multiply parentheses ..

-((+x^2-19x+9x-171))-28=0


We calculate terms in parentheses: -((+x^2-19x+9x-171)), so:

(+x^2-19x+9x-171)

We get rid of parentheses

x^2-19x+9x-171

We add all the numbers together, and all the variables

x^2-10x-171

Back to the equation:

-(x^2-10x-171)


We get rid of parentheses

-x^2+10x+171-28=0

We add all the numbers together, and all the variables

-1x^2+10x+143=0

a = -1; b = 10; c = +143;
Δ = b2-4ac
Δ = 102-4·(-1)·143
Δ = 672
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:

$\sqrt{\Delta}=\sqrt{672}=\sqrt{16*42}=\sqrt{16}*\sqrt{42}=4\sqrt{42}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(10)-4\sqrt{42}}{2*-1}=\frac{-10-4\sqrt{42}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(10)+4\sqrt{42}}{2*-1}=\frac{-10+4\sqrt{42}}{-2}
$