(3x-7)(9x+9)=0

Solution for (3x-7)(9x+9)=0 equation:

(3x-7)(9x+9)=0

We multiply parentheses ..

(+27x^2+27x-63x-63)=0

We get rid of parentheses

27x^2+27x-63x-63=0

We add all the numbers together, and all the variables

27x^2-36x-63=0

a = 27; b = -36; c = -63;
Δ = b2-4ac
Δ = -362-4·27·(-63)
Δ = 8100
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{8100}=90$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-36)-90}{2*27}=\frac{-54}{54}
=-1
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-36)+90}{2*27}=\frac{126}{54}
=2+1/3
$