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

Solution for 2+15x+(-8x^2)=0 equation:

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

We get rid of parentheses

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

a = -8; b = 15; c = +2;
Δ = b2-4ac
Δ = 152-4·(-8)·2
Δ = 289
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{289}=17$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(15)-17}{2*-8}=\frac{-32}{-16}
=+2
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(15)+17}{2*-8}=\frac{2}{-16}
=-1/8
$