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

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

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

We multiply parentheses ..

(+x^2-9x+7x-63)+(x-7)(x+9)=0

We get rid of parentheses

x^2-9x+7x+(x-7)(x+9)-63=0

We multiply parentheses ..

x^2+(+x^2+9x-7x-63)-9x+7x-63=0

We add all the numbers together, and all the variables

x^2+(+x^2+9x-7x-63)-2x-63=0

We get rid of parentheses

x^2+x^2+9x-7x-2x-63-63=0

We add all the numbers together, and all the variables

2x^2-126=0

a = 2; b = 0; c = -126;
Δ = b2-4ac
Δ = 02-4·2·(-126)
Δ = 1008
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{1008}=\sqrt{144*7}=\sqrt{144}*\sqrt{7}=12\sqrt{7}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-12\sqrt{7}}{2*2}=\frac{0-12\sqrt{7}}{4}
=-\frac{12\sqrt{7}}{4}
=-3\sqrt{7}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+12\sqrt{7}}{2*2}=\frac{0+12\sqrt{7}}{4}
=\frac{12\sqrt{7}}{4}
=3\sqrt{7}
$