135=(x+1)(x-5)

Solution for 135=(x+1)(x-5) equation:

135=(x+1)(x-5)

We move all terms to the left:

135-((x+1)(x-5))=0

We multiply parentheses ..

-((+x^2-5x+x-5))+135=0


We calculate terms in parentheses: -((+x^2-5x+x-5)), so:

(+x^2-5x+x-5)

We get rid of parentheses

x^2-5x+x-5

We add all the numbers together, and all the variables

x^2-4x-5

Back to the equation:

-(x^2-4x-5)


We get rid of parentheses

-x^2+4x+5+135=0

We add all the numbers together, and all the variables

-1x^2+4x+140=0

a = -1; b = 4; c = +140;
Δ = b2-4ac
Δ = 42-4·(-1)·140
Δ = 576
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{576}=24$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(4)-24}{2*-1}=\frac{-28}{-2}
=+14
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(4)+24}{2*-1}=\frac{20}{-2}
=-10
$