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

Solution for (-2x^2)+4x+9=0 equation:

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

We get rid of parentheses

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

a = -2; b = 4; c = +9;
Δ = b2-4ac
Δ = 42-4·(-2)·9
Δ = 88
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:

$\sqrt{\Delta}=\sqrt{88}=\sqrt{4*22}=\sqrt{4}*\sqrt{22}=2\sqrt{22}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(4)-2\sqrt{22}}{2*-2}=\frac{-4-2\sqrt{22}}{-4}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(4)+2\sqrt{22}}{2*-2}=\frac{-4+2\sqrt{22}}{-4}
$