4x(x+3)=20

Solution for 4x(x+3)=20 equation:

4x(x+3)=20

We move all terms to the left:

4x(x+3)-(20)=0

We multiply parentheses

4x^2+12x-20=0

a = 4; b = 12; c = -20;
Δ = b2-4ac
Δ = 122-4·4·(-20)
Δ = 464
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:

$\sqrt{\Delta}=\sqrt{464}=\sqrt{16*29}=\sqrt{16}*\sqrt{29}=4\sqrt{29}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(12)-4\sqrt{29}}{2*4}=\frac{-12-4\sqrt{29}}{8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(12)+4\sqrt{29}}{2*4}=\frac{-12+4\sqrt{29}}{8}
$