28r=4r^2

Solution for 28r=4r^2 equation:

28r=4r^2

We move all terms to the left:

28r-(4r^2)=0

determiningTheFunctionDomain
-4r^2+28r=0

a = -4; b = 28; c = 0;
Δ = b2-4ac
Δ = 282-4·(-4)·0
Δ = 784
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{784}=28$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(28)-28}{2*-4}=\frac{-56}{-8}
=+7
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(28)+28}{2*-4}=\frac{0}{-8}
=0
$