(7x+9)(7x-9)=40

Solution for (7x+9)(7x-9)=40 equation:

(7x+9)(7x-9)=40

We move all terms to the left:

(7x+9)(7x-9)-(40)=0

We use the square of the difference formula

49x^2-81-40=0

We add all the numbers together, and all the variables

49x^2-121=0

a = 49; b = 0; c = -121;
Δ = b2-4ac
Δ = 02-4·49·(-121)
Δ = 23716
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{23716}=154$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-154}{2*49}=\frac{-154}{98}
=-1+4/7
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+154}{2*49}=\frac{154}{98}
=1+4/7
$