20x^2-64x-21=0

Solution for 20x^2-64x-21=0 equation:

20x^2-64x-21=0

a = 20; b = -64; c = -21;
Δ = b2-4ac
Δ = -642-4·20·(-21)
Δ = 5776
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{5776}=76$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-64)-76}{2*20}=\frac{-12}{40}
=-3/10
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-64)+76}{2*20}=\frac{140}{40}
=3+1/2
$