18=-5x(-3x+15)

Solution for 18=-5x(-3x+15) equation:

18=-5x(-3x+15)

We move all terms to the left:

18-(-5x(-3x+15))=0


We calculate terms in parentheses: -(-5x(-3x+15)), so:

-5x(-3x+15)

We multiply parentheses

15x^2-75x

Back to the equation:

-(15x^2-75x)


We get rid of parentheses

-15x^2+75x+18=0

a = -15; b = 75; c = +18;
Δ = b2-4ac
Δ = 752-4·(-15)·18
Δ = 6705
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:

$\sqrt{\Delta}=\sqrt{6705}=\sqrt{9*745}=\sqrt{9}*\sqrt{745}=3\sqrt{745}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(75)-3\sqrt{745}}{2*-15}=\frac{-75-3\sqrt{745}}{-30}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(75)+3\sqrt{745}}{2*-15}=\frac{-75+3\sqrt{745}}{-30}
$