0=7x^2-4x-9

Solution for 0=7x^2-4x-9 equation:

0=7x^2-4x-9

We move all terms to the left:

0-(7x^2-4x-9)=0

We add all the numbers together, and all the variables

-(7x^2-4x-9)=0

We get rid of parentheses

-7x^2+4x+9=0

a = -7; b = 4; c = +9;
Δ = b2-4ac
Δ = 42-4·(-7)·9
Δ = 268
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:

$\sqrt{\Delta}=\sqrt{268}=\sqrt{4*67}=\sqrt{4}*\sqrt{67}=2\sqrt{67}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(4)-2\sqrt{67}}{2*-7}=\frac{-4-2\sqrt{67}}{-14}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(4)+2\sqrt{67}}{2*-7}=\frac{-4+2\sqrt{67}}{-14}
$