(x-)(x+9)=11

Solution for (x-)(x+9)=11 equation:

(x-)(x+9)=11

We move all terms to the left:

(x-)(x+9)-(11)=0

We add all the numbers together, and all the variables

(+x)(x+9)-11=0

We multiply parentheses ..

(+x^2+9x)-11=0

We get rid of parentheses

x^2+9x-11=0

a = 1; b = 9; c = -11;
Δ = b2-4ac
Δ = 92-4·1·(-11)
Δ = 125
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:

$\sqrt{\Delta}=\sqrt{125}=\sqrt{25*5}=\sqrt{25}*\sqrt{5}=5\sqrt{5}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(9)-5\sqrt{5}}{2*1}=\frac{-9-5\sqrt{5}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(9)+5\sqrt{5}}{2*1}=\frac{-9+5\sqrt{5}}{2}
$