9x=21x^2

Solution for 9x=21x^2 equation:

9x=21x^2

We move all terms to the left:

9x-(21x^2)=0

determiningTheFunctionDomain
-21x^2+9x=0

a = -21; b = 9; c = 0;
Δ = b2-4ac
Δ = 92-4·(-21)·0
Δ = 81
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{81}=9$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(9)-9}{2*-21}=\frac{-18}{-42}
=3/7
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(9)+9}{2*-21}=\frac{0}{-42}
=0
$