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

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

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

We move all terms to the left:

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

We add all the numbers together, and all the variables

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

We multiply parentheses ..

(+21x^2+21x-42x-42)=0

We get rid of parentheses

21x^2+21x-42x-42=0

We add all the numbers together, and all the variables

21x^2-21x-42=0

a = 21; b = -21; c = -42;
Δ = b2-4ac
Δ = -212-4·21·(-42)
Δ = 3969
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3969}=63$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-63}{2*21}=\frac{-42}{42}
=-1
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+63}{2*21}=\frac{84}{42}
=2
$