5x(4x-1)=15

Solution for 5x(4x-1)=15 equation:

5x(4x-1)=15

We move all terms to the left:

5x(4x-1)-(15)=0

We multiply parentheses

20x^2-5x-15=0

a = 20; b = -5; c = -15;
Δ = b2-4ac
Δ = -52-4·20·(-15)
Δ = 1225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1225}=35$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-5)-35}{2*20}=\frac{-30}{40}
=-3/4
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-5)+35}{2*20}=\frac{40}{40}
=1
$