(3x-3)(7x+2)=0

Solution for (3x-3)(7x+2)=0 equation:

(3x-3)(7x+2)=0

We multiply parentheses ..

(+21x^2+6x-21x-6)=0

We get rid of parentheses

21x^2+6x-21x-6=0

We add all the numbers together, and all the variables

21x^2-15x-6=0

a = 21; b = -15; c = -6;
Δ = b2-4ac
Δ = -152-4·21·(-6)
Δ = 729
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{729}=27$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-27}{2*21}=\frac{-12}{42}
=-2/7
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+27}{2*21}=\frac{42}{42}
=1
$