-2x2+8x+15=0

Solution for -2x2+8x+15=0 equation:

-2x^2+8x+15=0

a = -2; b = 8; c = +15;
Δ = b2-4ac
Δ = 82-4·(-2)·15
Δ = 184
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:

$\sqrt{\Delta}=\sqrt{184}=\sqrt{4*46}=\sqrt{4}*\sqrt{46}=2\sqrt{46}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(8)-2\sqrt{46}}{2*-2}=\frac{-8-2\sqrt{46}}{-4}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(8)+2\sqrt{46}}{2*-2}=\frac{-8+2\sqrt{46}}{-4}
$