7u^2-4u-8=0

Solution for 7u^2-4u-8=0 equation:

7u^2-4u-8=0

a = 7; b = -4; c = -8;
Δ = b2-4ac
Δ = -42-4·7·(-8)
Δ = 240
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{240}=\sqrt{16*15}=\sqrt{16}*\sqrt{15}=4\sqrt{15}$
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-4)-4\sqrt{15}}{2*7}=\frac{4-4\sqrt{15}}{14}
$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-4)+4\sqrt{15}}{2*7}=\frac{4+4\sqrt{15}}{14}
$