Is this a function or no function? y=x2

  In order to find out whether something is a function or not, you can choose to graph the equation or find out using other methods. If the equation passes the vertical line test, such that each x value has only one corresponding y value, then the equation is a function. In other words, something is a function only if each of its inputs has only one output. You can find out whether the equation is a function through substituting values into the equation or finding the table of the graph of the equation. The simplest method available if you have a graphing calculator is to just draw a straight line above any x-value. If there's only one point on the graph that has that x-value, then the equation you're talking about is a function. If not, then it's not a function.