Expert: Scott A Wilson - 9/22/2010

Question
while trying to sketch a graph for Y=sgrt16-xsq.  Icame up withx=+/- (4,0)and (y=+/- (4,0).  The book came up with
(0,4), (4,0),(-4,0) They did not get  (0,-4). Where did I go wrong? Scott, I asked this question back on 9-12, since then I have purchased a Ti 84 calculator and it got the same answer as the book. their graph is a semi circle and ours is a full circle. any ideas why??

Answer
When y = √(16-x²), the squareroot is always assumed to be positive.
That is why in the quadratic equation is has a +/- in the middle of it.  It assumed the squareroot is taken as the positive value and wants to make it known that it is plus or minus.

This is because the squareroot is considered to be a function,
there can be only one y value for any x value.  In this way, if a negative squareroot is wanted, they put a negative sign out front.