-2r^2-7r=0

Solution for -2r^2-7r=0 equation:

-2r^2-7r=0

a = -2; b = -7; c = 0;
Δ = b2-4ac
Δ = -72-4·(-2)·0
Δ = 49
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{49}=7$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-7)-7}{2*-2}=\frac{0}{-4}
=0
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-7)+7}{2*-2}=\frac{14}{-4}
=-3+1/2
$