-70-4r+2r^2=0

Solution for -70-4r+2r^2=0 equation:

-70-4r+2r^2=0

a = 2; b = -4; c = -70;
Δ = b2-4ac
Δ = -42-4·2·(-70)
Δ = 576
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{576}=24$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-4)-24}{2*2}=\frac{-20}{4}
=-5
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-4)+24}{2*2}=\frac{28}{4}
=7
$