4x(x+5)=15

Solution for 4x(x+5)=15 equation:

4x(x+5)=15

We move all terms to the left:

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

We multiply parentheses

4x^2+20x-15=0

a = 4; b = 20; c = -15;
Δ = b2-4ac
Δ = 202-4·4·(-15)
Δ = 640
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:

$\sqrt{\Delta}=\sqrt{640}=\sqrt{64*10}=\sqrt{64}*\sqrt{10}=8\sqrt{10}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(20)-8\sqrt{10}}{2*4}=\frac{-20-8\sqrt{10}}{8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(20)+8\sqrt{10}}{2*4}=\frac{-20+8\sqrt{10}}{8}
$