Read the Graph of a Function


Here is how to read the graph:

  • To find $f(3)$, go to 3 on the x-axis, up or down until you hit the curve, then straight across to the y-axis. That is the height of the curve above 3.
  • The x-intercepts are where the curve crosses the x-axis, so they are the values of x with $f(x) = 0$. The y-intercept is the single height $f(0)$.
  • $f(x) > 0$ where the curve is above the axis and $f(x) < 0$ where it is below. The curve changes side only at an x-intercept.
  • The domain is how far the graph reaches from left to right, the range how far it reaches from bottom to top - so the range runs from the lowest point of the curve to the highest.
  • To count how often the line $y = c$ meets the graph, draw that level line across the picture and count the crossings. An upright line $x = a$ can meet it at most once, because a function has only one value for each x - that is the vertical line test.
  • Increasing means the curve rises as you read from left to right, decreasing means it falls.

Reload the page and you get a new worksheet - both graphs are generated at random every time.

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