224=3.5r^2

Solution for 224=3.5r^2 equation:

224=3.5r^2

We move all terms to the left:

224-(3.5r^2)=0

We get rid of parentheses

-3.5r^2+224=0

a = -3.5; b = 0; c = +224;
Δ = b2-4ac
Δ = 02-4·(-3.5)·224
Δ = 3136
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3136}=56$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-56}{2*-3.5}=\frac{-56}{-7}
=+8
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+56}{2*-3.5}=\frac{56}{-7}
=-8
$