(x+5)(x+11)=391

Solution for (x+5)(x+11)=391 equation:

(x+5)(x+11)=391

We move all terms to the left:

(x+5)(x+11)-(391)=0

We multiply parentheses ..

(+x^2+11x+5x+55)-391=0

We get rid of parentheses

x^2+11x+5x+55-391=0

We add all the numbers together, and all the variables

x^2+16x-336=0

a = 1; b = 16; c = -336;
Δ = b2-4ac
Δ = 162-4·1·(-336)
Δ = 1600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1600}=40$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(16)-40}{2*1}=\frac{-56}{2}
=-28
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(16)+40}{2*1}=\frac{24}{2}
=12
$