(2-z)(2z+9)=0

Solution for (2-z)(2z+9)=0 equation:

(2-z)(2z+9)=0

We add all the numbers together, and all the variables

(-1z+2)(2z+9)=0

We multiply parentheses ..

(-2z^2-9z+4z+18)=0

We get rid of parentheses

-2z^2-9z+4z+18=0

We add all the numbers together, and all the variables

-2z^2-5z+18=0

a = -2; b = -5; c = +18;
Δ = b2-4ac
Δ = -52-4·(-2)·18
Δ = 169
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$z_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$z_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{169}=13$
$z_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-5)-13}{2*-2}=\frac{-8}{-4}
=+2
$
$z_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-5)+13}{2*-2}=\frac{18}{-4}
=-4+1/2
$