20x^2+6x-21=0

Solution for 20x^2+6x-21=0 equation:

20x^2+6x-21=0

a = 20; b = 6; c = -21;
Δ = b2-4ac
Δ = 62-4·20·(-21)
Δ = 1716
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{1716}=\sqrt{4*429}=\sqrt{4}*\sqrt{429}=2\sqrt{429}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(6)-2\sqrt{429}}{2*20}=\frac{-6-2\sqrt{429}}{40}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(6)+2\sqrt{429}}{2*20}=\frac{-6+2\sqrt{429}}{40}
$