3x(x+4)-11=28

Solution for 3x(x+4)-11=28 equation:

3x(x+4)-11=28

We move all terms to the left:

3x(x+4)-11-(28)=0

We add all the numbers together, and all the variables

3x(x+4)-39=0

We multiply parentheses

3x^2+12x-39=0

a = 3; b = 12; c = -39;
Δ = b2-4ac
Δ = 122-4·3·(-39)
Δ = 612
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:

$\sqrt{\Delta}=\sqrt{612}=\sqrt{36*17}=\sqrt{36}*\sqrt{17}=6\sqrt{17}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(12)-6\sqrt{17}}{2*3}=\frac{-12-6\sqrt{17}}{6}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(12)+6\sqrt{17}}{2*3}=\frac{-12+6\sqrt{17}}{6}
$