-5x(x-3)=-40

Solution for -5x(x-3)=-40 equation:

-5x(x-3)=-40

We move all terms to the left:

-5x(x-3)-(-40)=0

We add all the numbers together, and all the variables

-5x(x-3)+40=0

We multiply parentheses

-5x^2+15x+40=0

a = -5; b = 15; c = +40;
Δ = b2-4ac
Δ = 152-4·(-5)·40
Δ = 1025
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:

$\sqrt{\Delta}=\sqrt{1025}=\sqrt{25*41}=\sqrt{25}*\sqrt{41}=5\sqrt{41}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(15)-5\sqrt{41}}{2*-5}=\frac{-15-5\sqrt{41}}{-10}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(15)+5\sqrt{41}}{2*-5}=\frac{-15+5\sqrt{41}}{-10}
$