21y=6y^2

Solution for 21y=6y^2 equation:

21y=6y^2

We move all terms to the left:

21y-(6y^2)=0

determiningTheFunctionDomain
-6y^2+21y=0

a = -6; b = 21; c = 0;
Δ = b2-4ac
Δ = 212-4·(-6)·0
Δ = 441
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{441}=21$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(21)-21}{2*-6}=\frac{-42}{-12}
=3+1/2
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(21)+21}{2*-6}=\frac{0}{-12}
=0
$