You do the vertical line test. Look at the graph to see if for an x-value, there are multiple y's associated with it.
See: http://www.regentsprep.org/regents/math/algebra/ap3/lfunction.htm
You do the vertical line test. Look at the graph to see if for an x-value, there are multiple y's associated with it.
See: http://www.regentsprep.org/regents/math/algebra/ap3/lfunction.htm