4x(x+3)=40

Solution for 4x(x+3)=40 equation:

4x(x+3)=40

We move all terms to the left:

4x(x+3)-(40)=0

We multiply parentheses

4x^2+12x-40=0

a = 4; b = 12; c = -40;
Δ = b2-4ac
Δ = 122-4·4·(-40)
Δ = 784
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{784}=28$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(12)-28}{2*4}=\frac{-40}{8}
=-5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(12)+28}{2*4}=\frac{16}{8}
=2
$