There are five sign changes, so there are five or, counting down in pairs, three or one negative solutions. Then my answer is:There are two or zero positive solutions, and five, three, or one negative solutions.In the above example, the maximum number of positive solutions (two) and the maximum number of negative solutions (five) added up to the leading degree (seven). It will always be true that the sum of the possible numbers of positive and negative solutions will be equal to the degree of the polynomial, or two less, or four less, or....This can be helpful for checking your work. For instance, if I had come up with a maximum answer of "two" for the possible positive solutions in the above example but had come up with only, say, "four" for the possible negative solutions, then I would have known that I had made a mistake somewhere, because 2 + 4 does not equal 7, or 5, or 3, or 1
There are four, two, or zero positive roots, and zero negative roots.
Descartes' Rule of Signs can be useful for helping you figure out (if you don't have a graphing calculator that can show you) where to look for the zeroes of a polynomial. For instance, suppose the Rational Roots Test gives you a long list of potential zeroes, you've found one negative zero, and the Rule of Signs says that there is at most one negative root. Then you know that you've found every possible negative root (rational or otherwise), so you should now start looking at potential positive roots.Similarly, if you've found, say, two positive solutions, and the Rule of Signs says that you should have, say, five or three or one positive solutions, then you know that, since you've found two, there is at least one more (to take you up to three), and maybe three more (to take you up to five), so you should keep looking for a positive solution.