8r^2-4=644

Solution for 8r^2-4=644 equation:

8r^2-4=644

We move all terms to the left:

8r^2-4-(644)=0

We add all the numbers together, and all the variables

8r^2-648=0

a = 8; b = 0; c = -648;
Δ = b2-4ac
Δ = 02-4·8·(-648)
Δ = 20736
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{20736}=144$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-144}{2*8}=\frac{-144}{16}
=-9
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+144}{2*8}=\frac{144}{16}
=9
$