4b^2-8b-15=0

Solution for 4b^2-8b-15=0 equation:

4b^2-8b-15=0

a = 4; b = -8; c = -15;
Δ = b2-4ac
Δ = -82-4·4·(-15)
Δ = 304
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{304}=\sqrt{16*19}=\sqrt{16}*\sqrt{19}=4\sqrt{19}$
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-8)-4\sqrt{19}}{2*4}=\frac{8-4\sqrt{19}}{8}
$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-8)+4\sqrt{19}}{2*4}=\frac{8+4\sqrt{19}}{8}
$