Question

Which equation defines a function?
a. x= |y|
b. y=[[x]]
c. x=1/8y^2
d. x^2+y^2=49

Answer 1

Remember that a function can have ONE value for every y value. Do the vertical line test. Graph the equation and if more than ONE point goes through any part of the graph, it is NOT a function.

Try this vertical line test on this function (your last one):

http://www.wolframalpha.com/input/?i=x%5E2%2By%5E2%3D49

Answer 2

So the last one doesn't work since it is a circle.

Answer 3

a is just a line
c is a parabola