(x+3)(7x-6)=0

Solution for (x+3)(7x-6)=0 equation:

(x+3)(7x-6)=0

We multiply parentheses ..

(+7x^2-6x+21x-18)=0

We get rid of parentheses

7x^2-6x+21x-18=0

We add all the numbers together, and all the variables

7x^2+15x-18=0

a = 7; b = 15; c = -18;
Δ = b2-4ac
Δ = 152-4·7·(-18)
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*7}=\frac{-42}{14}
=-3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(15)+27}{2*7}=\frac{12}{14}
=6/7
$