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

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

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

We multiply parentheses ..

(+9x^2+63x-3x-21)=0

We get rid of parentheses

9x^2+63x-3x-21=0

We add all the numbers together, and all the variables

9x^2+60x-21=0

a = 9; b = 60; c = -21;
Δ = b2-4ac
Δ = 602-4·9·(-21)
Δ = 4356
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{4356}=66$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(60)-66}{2*9}=\frac{-126}{18}
=-7
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(60)+66}{2*9}=\frac{6}{18}
=1/3
$