Trees grow faster and form wider rings in warm years and grow more slowly and form narrower rings in cooler years. The figure shows ring widths of a Siberian pine from 1500 to 2000.
(a) What is the range of the ring width function?
(b) What does the graph tend to say about the temperature of the earth? Does the graph reflect the volcanic eruptions of the mid-19th century?
okay. Is this the graph of a function? Well, remember that a function must pass the vertical line test, which means that for every X value there's only one y value. So if you pass a vertical line through, it can only pass through one point. This vertical line passes through only one point, and so does this one. However, this vertical line passes through multiple points, as does this one and this one. And even though there are some vertical lines that pass through only one point, if there exists any vertical lines that pass through multiple points, it's not a function.