4x(-5x)=-13

Solution for 4x(-5x)=-13 equation:

4x(-5x)=-13

We move all terms to the left:

4x(-5x)-(-13)=0

We add all the numbers together, and all the variables

4x(-5x)+13=0

We multiply parentheses

-20x^2+13=0

a = -20; b = 0; c = +13;
Δ = b2-4ac
Δ = 02-4·(-20)·13
Δ = 1040
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:

$\sqrt{\Delta}=\sqrt{1040}=\sqrt{16*65}=\sqrt{16}*\sqrt{65}=4\sqrt{65}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-4\sqrt{65}}{2*-20}=\frac{0-4\sqrt{65}}{-40}
=-\frac{4\sqrt{65}}{-40}
=-\frac{\sqrt{65}}{-10}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+4\sqrt{65}}{2*-20}=\frac{0+4\sqrt{65}}{-40}
=\frac{4\sqrt{65}}{-40}
=\frac{\sqrt{65}}{-10}
$