u^2-21=12

Solution for u^2-21=12 equation:

u^2-21=12

We move all terms to the left:

u^2-21-(12)=0

We add all the numbers together, and all the variables

u^2-33=0

a = 1; b = 0; c = -33;
Δ = b2-4ac
Δ = 02-4·1·(-33)
Δ = 132
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{132}=\sqrt{4*33}=\sqrt{4}*\sqrt{33}=2\sqrt{33}$
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-2\sqrt{33}}{2*1}=\frac{0-2\sqrt{33}}{2}
=-\frac{2\sqrt{33}}{2}
=-\sqrt{33}
$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+2\sqrt{33}}{2*1}=\frac{0+2\sqrt{33}}{2}
=\frac{2\sqrt{33}}{2}
=\sqrt{33}
$