Are you sure it is 16-Y^2? not X^2
anyway i graphed X^2 and it looks like a bowl upside down
If the equation is
Then recall that the equation of a circle is
If you re-arrange for y, then you get your equation, but only the positive half.
The OP fixed the mistake by posting again. It's actually . This is a semicircle centred at the origin of radius 4 units, taking on only positive values for x.