(X+7)(x-9)+(x-7)(x+9)+76=0

Solution for (X+7)(x-9)+(x-7)(x+9)+76=0 equation:

(X+7)(X-9)+(X-7)(X+9)+76=0

We multiply parentheses ..

(+X^2-9X+7X-63)+(X-7)(X+9)+76=0

We get rid of parentheses

X^2-9X+7X+(X-7)(X+9)-63+76=0

We multiply parentheses ..

X^2+(+X^2+9X-7X-63)-9X+7X-63+76=0

We add all the numbers together, and all the variables

X^2+(+X^2+9X-7X-63)-2X+13=0

We get rid of parentheses

X^2+X^2+9X-7X-2X-63+13=0

We add all the numbers together, and all the variables

2X^2-50=0

a = 2; b = 0; c = -50;
Δ = b2-4ac
Δ = 02-4·2·(-50)
Δ = 400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{400}=20$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-20}{2*2}=\frac{-20}{4}
=-5
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+20}{2*2}=\frac{20}{4}
=5
$