-8a^2-14a+15=0

Solution for -8a^2-14a+15=0 equation:

-8a^2-14a+15=0

a = -8; b = -14; c = +15;
Δ = b2-4ac
Δ = -142-4·(-8)·15
Δ = 676
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{676}=26$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-14)-26}{2*-8}=\frac{-12}{-16}
=3/4
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-14)+26}{2*-8}=\frac{40}{-16}
=-2+1/2
$