7u^2+21u-35=0

Solution for 7u^2+21u-35=0 equation:

7u^2+21u-35=0

a = 7; b = 21; c = -35;
Δ = b2-4ac
Δ = 212-4·7·(-35)
Δ = 1421
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:

$\sqrt{\Delta}=\sqrt{1421}=\sqrt{49*29}=\sqrt{49}*\sqrt{29}=7\sqrt{29}$
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(21)-7\sqrt{29}}{2*7}=\frac{-21-7\sqrt{29}}{14}
$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(21)+7\sqrt{29}}{2*7}=\frac{-21+7\sqrt{29}}{14}
$