3x^2-14x-21=0

Solution for 3x^2-14x-21=0 equation:

3x^2-14x-21=0

a = 3; b = -14; c = -21;
Δ = b2-4ac
Δ = -142-4·3·(-21)
Δ = 448
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:

$\sqrt{\Delta}=\sqrt{448}=\sqrt{64*7}=\sqrt{64}*\sqrt{7}=8\sqrt{7}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-14)-8\sqrt{7}}{2*3}=\frac{14-8\sqrt{7}}{6}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-14)+8\sqrt{7}}{2*3}=\frac{14+8\sqrt{7}}{6}
$