-7=18x+9x^2=0

Solution for -7=18x+9x^2=0 equation:

-7=18x+9x^2=0

We move all terms to the left:

-7-(18x+9x^2)=0

We get rid of parentheses

-9x^2-18x-7=0

a = -9; b = -18; c = -7;
Δ = b2-4ac
Δ = -182-4·(-9)·(-7)
Δ = 72
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:

$\sqrt{\Delta}=\sqrt{72}=\sqrt{36*2}=\sqrt{36}*\sqrt{2}=6\sqrt{2}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-18)-6\sqrt{2}}{2*-9}=\frac{18-6\sqrt{2}}{-18}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-18)+6\sqrt{2}}{2*-9}=\frac{18+6\sqrt{2}}{-18}
$