(3-z)(3z+7)=0

Solution for (3-z)(3z+7)=0 equation:

(3-z)(3z+7)=0

We add all the numbers together, and all the variables

(-1z+3)(3z+7)=0

We multiply parentheses ..

(-3z^2-7z+9z+21)=0

We get rid of parentheses

-3z^2-7z+9z+21=0

We add all the numbers together, and all the variables

-3z^2+2z+21=0

a = -3; b = 2; c = +21;
Δ = b2-4ac
Δ = 22-4·(-3)·21
Δ = 256
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$z_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$z_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{256}=16$
$z_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(2)-16}{2*-3}=\frac{-18}{-6}
=+3
$
$z_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(2)+16}{2*-3}=\frac{14}{-6}
=-2+1/3
$