(x+3)(x+6)=60

Solution for (x+3)(x+6)=60 equation:

(x+3)(x+6)=60

We move all terms to the left:

(x+3)(x+6)-(60)=0

We multiply parentheses ..

(+x^2+6x+3x+18)-60=0

We get rid of parentheses

x^2+6x+3x+18-60=0

We add all the numbers together, and all the variables

x^2+9x-42=0

a = 1; b = 9; c = -42;
Δ = b2-4ac
Δ = 92-4·1·(-42)
Δ = 249
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(9)-\sqrt{249}}{2*1}=\frac{-9-\sqrt{249}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(9)+\sqrt{249}}{2*1}=\frac{-9+\sqrt{249}}{2}
$