3(45+x)(2+x)=720

Solution for 3(45+x)(2+x)=720 equation:

3(45+x)(2+x)=720

We move all terms to the left:

3(45+x)(2+x)-(720)=0

We add all the numbers together, and all the variables

3(x+45)(x+2)-720=0

We multiply parentheses ..

3(+x^2+2x+45x+90)-720=0

We multiply parentheses

3x^2+6x+135x+270-720=0

We add all the numbers together, and all the variables

3x^2+141x-450=0

a = 3; b = 141; c = -450;
Δ = b2-4ac
Δ = 1412-4·3·(-450)
Δ = 25281
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{25281}=159$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(141)-159}{2*3}=\frac{-300}{6}
=-50
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(141)+159}{2*3}=\frac{18}{6}
=3
$