X*y=399

Solution for X*y=399 equation:

X*X=399

We move all terms to the left:

X*X-(399)=0

Wy multiply elements

X^2-399=0

a = 1; b = 0; c = -399;
Δ = b2-4ac
Δ = 02-4·1·(-399)
Δ = 1596
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:

$\sqrt{\Delta}=\sqrt{1596}=\sqrt{4*399}=\sqrt{4}*\sqrt{399}=2\sqrt{399}$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-2\sqrt{399}}{2*1}=\frac{0-2\sqrt{399}}{2}
=-\frac{2\sqrt{399}}{2}
=-\sqrt{399}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+2\sqrt{399}}{2*1}=\frac{0+2\sqrt{399}}{2}
=\frac{2\sqrt{399}}{2}
=\sqrt{399}
$