ELI5: Explain Like I'm 5

Routh's theorem

Okay, kiddo, let's talk about Routh's Theorem. Imagine you have a big math problem that has a polynomial equation with several variables. You want to know if the equation has any roots (or solutions), which are just numbers that make the equation true.

Routh's Theorem helps us figure out if any of these roots are negative. You see, if any of the roots are negative, then that means the problem has a real-world significance that isn't good - maybe something like the height of a rocket or the depth of a submarine. Negative numbers usually mean we're going in the wrong direction!

To use Routh's Theorem, we first have to write out our polynomial in a specific way. We take the equation and break it apart into smaller chunks, each with a different variable. We write these chunks down in rows, with the first row being the highest-degree chunk, and the last row being the lowest-degree chunk.

Then, we create two new rows. In the first new row, we write down the coefficients of every other chunk in the equation, starting with the first chunk in the top row. In the second new row, we write down the coefficients of the remaining chunks.

Next, we look at the first column of our new rows. If any of the entries are negative, then that means the polynomial has at least one negative root. If all of the entries are positive, then all of the roots are positive (or zero).

And that's basically what Routh's Theorem does - it helps us check if a polynomial equation has any negative roots. It might seem complicated, but it can be really useful when we're working on more complex math problems.