180=(4x-15)(x+9)

Solution for 180=(4x-15)(x+9) equation:

180=(4x-15)(x+9)

We move all terms to the left:

180-((4x-15)(x+9))=0

We multiply parentheses ..

-((+4x^2+36x-15x-135))+180=0


We calculate terms in parentheses: -((+4x^2+36x-15x-135)), so:

(+4x^2+36x-15x-135)

We get rid of parentheses

4x^2+36x-15x-135

We add all the numbers together, and all the variables

4x^2+21x-135

Back to the equation:

-(4x^2+21x-135)


We get rid of parentheses

-4x^2-21x+135+180=0

We add all the numbers together, and all the variables

-4x^2-21x+315=0

a = -4; b = -21; c = +315;
Δ = b2-4ac
Δ = -212-4·(-4)·315
Δ = 5481
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:

$\sqrt{\Delta}=\sqrt{5481}=\sqrt{9*609}=\sqrt{9}*\sqrt{609}=3\sqrt{609}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-3\sqrt{609}}{2*-4}=\frac{21-3\sqrt{609}}{-8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+3\sqrt{609}}{2*-4}=\frac{21+3\sqrt{609}}{-8}
$