(k+11)(k+15)=0

Solution for (k+11)(k+15)=0 equation:

(k+11)(k+15)=0

We multiply parentheses ..

(+k^2+15k+11k+165)=0

We get rid of parentheses

k^2+15k+11k+165=0

We add all the numbers together, and all the variables

k^2+26k+165=0

a = 1; b = 26; c = +165;
Δ = b2-4ac
Δ = 262-4·1·165
Δ = 16
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$k_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$k_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{16}=4$
$k_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(26)-4}{2*1}=\frac{-30}{2}
=-15
$
$k_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(26)+4}{2*1}=\frac{-22}{2}
=-11
$