(3x^2/3)-21=0

Solution for (3x^2/3)-21=0 equation:

(3x^2/3)-21=0

We get rid of parentheses

3x^2/3-21=0

We multiply all the terms by the denominator


3x^2-21*3=0

We add all the numbers together, and all the variables

3x^2-63=0

a = 3; b = 0; c = -63;
Δ = b2-4ac
Δ = 02-4·3·(-63)
Δ = 756
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{756}=\sqrt{36*21}=\sqrt{36}*\sqrt{21}=6\sqrt{21}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-6\sqrt{21}}{2*3}=\frac{0-6\sqrt{21}}{6}
=-\frac{6\sqrt{21}}{6}
=-\sqrt{21}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+6\sqrt{21}}{2*3}=\frac{0+6\sqrt{21}}{6}
=\frac{6\sqrt{21}}{6}
=\sqrt{21}
$