(m+8)(m-2)=-15

Solution for (m+8)(m-2)=-15 equation:

(m+8)(m-2)=-15

We move all terms to the left:

(m+8)(m-2)-(-15)=0

We add all the numbers together, and all the variables

(m+8)(m-2)+15=0

We multiply parentheses ..

(+m^2-2m+8m-16)+15=0

We get rid of parentheses

m^2-2m+8m-16+15=0

We add all the numbers together, and all the variables

m^2+6m-1=0

a = 1; b = 6; c = -1;
Δ = b2-4ac
Δ = 62-4·1·(-1)
Δ = 40
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$m_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$m_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{40}=\sqrt{4*10}=\sqrt{4}*\sqrt{10}=2\sqrt{10}$
$m_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(6)-2\sqrt{10}}{2*1}=\frac{-6-2\sqrt{10}}{2}
$
$m_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(6)+2\sqrt{10}}{2*1}=\frac{-6+2\sqrt{10}}{2}
$