7x^2-8x-28=0

Solution for 7x^2-8x-28=0 equation:

7x^2-8x-28=0

a = 7; b = -8; c = -28;
Δ = b2-4ac
Δ = -82-4·7·(-28)
Δ = 848
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:

$\sqrt{\Delta}=\sqrt{848}=\sqrt{16*53}=\sqrt{16}*\sqrt{53}=4\sqrt{53}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-8)-4\sqrt{53}}{2*7}=\frac{8-4\sqrt{53}}{14}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-8)+4\sqrt{53}}{2*7}=\frac{8+4\sqrt{53}}{14}
$