3r^2-24=21r

Solution for 3r^2-24=21r equation:

3r^2-24=21r

We move all terms to the left:

3r^2-24-(21r)=0

a = 3; b = -21; c = -24;
Δ = b2-4ac
Δ = -212-4·3·(-24)
Δ = 729
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{729}=27$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-27}{2*3}=\frac{-6}{6}
=-1
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+27}{2*3}=\frac{48}{6}
=8
$