(X+7)(x+11)=77

Solution for (X+7)(x+11)=77 equation:

(X+7)(X+11)=77

We move all terms to the left:

(X+7)(X+11)-(77)=0

We multiply parentheses ..

(+X^2+11X+7X+77)-77=0

We get rid of parentheses

X^2+11X+7X+77-77=0

We add all the numbers together, and all the variables

X^2+18X=0

a = 1; b = 18; c = 0;
Δ = b2-4ac
Δ = 182-4·1·0
Δ = 324
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{324}=18$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(18)-18}{2*1}=\frac{-36}{2}
=-18
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(18)+18}{2*1}=\frac{0}{2}
=0
$