(z+1)(-z+7)=0

Solution for (z+1)(-z+7)=0 equation:

(z+1)(-z+7)=0

We add all the numbers together, and all the variables

(z+1)(-1z+7)=0

We multiply parentheses ..

(-1z^2+7z-1z+7)=0

We get rid of parentheses

-1z^2+7z-1z+7=0

We add all the numbers together, and all the variables

-1z^2+6z+7=0

a = -1; b = 6; c = +7;
Δ = b2-4ac
Δ = 62-4·(-1)·7
Δ = 64
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$z_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$z_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{64}=8$
$z_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(6)-8}{2*-1}=\frac{-14}{-2}
=+7
$
$z_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(6)+8}{2*-1}=\frac{2}{-2}
=-1
$