3x(x+4)-5=26

Solution for 3x(x+4)-5=26 equation:

3x(x+4)-5=26

We move all terms to the left:

3x(x+4)-5-(26)=0

We add all the numbers together, and all the variables

3x(x+4)-31=0

We multiply parentheses

3x^2+12x-31=0

a = 3; b = 12; c = -31;
Δ = b2-4ac
Δ = 122-4·3·(-31)
Δ = 516
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:

$\sqrt{\Delta}=\sqrt{516}=\sqrt{4*129}=\sqrt{4}*\sqrt{129}=2\sqrt{129}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(12)-2\sqrt{129}}{2*3}=\frac{-12-2\sqrt{129}}{6}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(12)+2\sqrt{129}}{2*3}=\frac{-12+2\sqrt{129}}{6}
$