ELI5: Explain Like I'm 5

Cromwell's rule

Okay kiddo, let me explain Cromwell's rule in simple words. It's a math rule that helps us figure out if a mathematical equation or expression has a root, which means a value that makes the equation or expression equal to zero.

Imagine you have a very complicated equation, and you want to know if there is a number that makes it equal to zero. Cromwell's rule says that if you multiply all the coefficients of the polynomial by -1, and then arrange them in descending order, the number you get is the upper bound of the positive roots of the equation.

Umm, I know this sounds a bit confusing, so let me break it down.

A polynomial is just a fancy word for an equation that has some different terms added, subtracted, or multiplied together. For example, (2x^2 + 3x - 1) is a polynomial.

The coefficients are the numbers that are multiplied by the variables in the equation. In this case, 2, 3, and -1 are the coefficients.

Now, to use Cromwell's rule, we take all the coefficients and make them negative. So, in our example, we would get (-2x^2 -3x +1). Then we arrange them in descending order, which means we put the highest power of x first, then the second highest, and so on. This would look like this: (-2x^2 -3x +1).

Finally, the upper bound of the positive roots is the biggest positive number that can be a root of the equation. So, for our example, the upper bound of the positive roots would be 1.5 (you can check this by using other methods, like plotting the equation on a graph).

So, there you have it, Cromwell's rule in simple terms. It helps us find the upper bound of the positive roots of a polynomial equation.
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