39=(3x+4)x

Solution for 39=(3x+4)x equation:

39=(3x+4)x

We move all terms to the left:

39-((3x+4)x)=0


We calculate terms in parentheses: -((3x+4)x), so:

(3x+4)x

We multiply parentheses

3x^2+4x

Back to the equation:

-(3x^2+4x)


We get rid of parentheses

-3x^2-4x+39=0

a = -3; b = -4; c = +39;
Δ = b2-4ac
Δ = -42-4·(-3)·39
Δ = 484
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{484}=22$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-4)-22}{2*-3}=\frac{-18}{-6}
=+3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-4)+22}{2*-3}=\frac{26}{-6}
=-4+1/3
$