15b^2+4b-15=0

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

15b^2+4b-15=0

a = 15; b = 4; c = -15;
Δ = b2-4ac
Δ = 42-4·15·(-15)
Δ = 916
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:

$\sqrt{\Delta}=\sqrt{916}=\sqrt{4*229}=\sqrt{4}*\sqrt{229}=2\sqrt{229}$
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(4)-2\sqrt{229}}{2*15}=\frac{-4-2\sqrt{229}}{30}
$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(4)+2\sqrt{229}}{2*15}=\frac{-4+2\sqrt{229}}{30}
$