90=(6x)(x+13)

Solution for 90=(6x)(x+13) equation:

90=(6x)(x+13)

We move all terms to the left:

90-((6x)(x+13))=0


We calculate terms in parentheses: -(6x(x+13)), so:

6x(x+13)

We multiply parentheses

6x^2+78x

Back to the equation:

-(6x^2+78x)


We get rid of parentheses

-6x^2-78x+90=0

a = -6; b = -78; c = +90;
Δ = b2-4ac
Δ = -782-4·(-6)·90
Δ = 8244
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:

$\sqrt{\Delta}=\sqrt{8244}=\sqrt{36*229}=\sqrt{36}*\sqrt{229}=6\sqrt{229}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-78)-6\sqrt{229}}{2*-6}=\frac{78-6\sqrt{229}}{-12}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-78)+6\sqrt{229}}{2*-6}=\frac{78+6\sqrt{229}}{-12}
$