2b^2-15b-25=0

Solution for 2b^2-15b-25=0 equation:

2b^2-15b-25=0

a = 2; b = -15; c = -25;
Δ = b2-4ac
Δ = -152-4·2·(-25)
Δ = 425
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:

$\sqrt{\Delta}=\sqrt{425}=\sqrt{25*17}=\sqrt{25}*\sqrt{17}=5\sqrt{17}$
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-5\sqrt{17}}{2*2}=\frac{15-5\sqrt{17}}{4}
$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+5\sqrt{17}}{2*2}=\frac{15+5\sqrt{17}}{4}
$