20z^2-10z-3.75=0

Solution for 20z^2-10z-3.75=0 equation:

20z^2-10z-3.75=0

a = 20; b = -10; c = -3.75;
Δ = b2-4ac
Δ = -102-4·20·(-3.75)
Δ = 400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$z_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$z_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{400}=20$
$z_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-10)-20}{2*20}=\frac{-10}{40}
=-1/4
$
$z_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-10)+20}{2*20}=\frac{30}{40}
=3/4
$