This is the equation of this ellipse:



An ellipse is NOT a function because it does not pass the
vertical line test.

However the upper half of the ellipse is a function:



Also the lower half of the ellipse is a function:



To find these two functions we solve the equation for y:




Multiply through by LCD = 100






 = ±

When we use the positive sign we get the
functional equation

 = 

which is the equation of the top half of
the ellipse.

When we use the negative sign we get the
functional equation

 = 

which is the equation of the bottom half of
the ellipse.

Edwin