Tag: factoring

  • How to Use Prime Factoring to Win Friends and Influence People

    How to Use Prime Factoring to Win Friends and Influence People

    Alright, you might not win friends with this, but the more you can do arithmetic in your head… well… okay, you can’t influence people with it either. Regardless, it’s handy to know and helps with multiplication.

    Yesterday I posted a couple of videos about factoring numbers into primes. Now it’s time to put those to work.

    How about a rather simple one to get us started:

    Here’s one that’s a little more challenging. The key is that you can combine the bits to something you’re more comfortable doing. I don’t like multiplying nines, so I avoid those.

    Can you use this? Why or why not? Ha ha, just kidding – no essay questions here! – but if you do find a use for this, or if this annoys you, let me know in the comments.

  • 2 Ways to Factor Numbers into Primes

    2 Ways to Factor Numbers into Primes

    Factoring is traditionally considered an “f-word” for students of math. But it sometimes has its good sides (which I’ll show over the next couple of days).

    In the meantime, I’ll show the two ways (that I know) to factor numbers.

    This method’s called a factor tree:

    You don’t have to put the primes in order for it to be “right.” But it helps for later things.

    Here’s another tree:

    Here’s another way to factor using an upside division bar-type thing:

    Remember, we don’t factor for the sake of factoring. This is only a tool to use when we do other stuff. You’ll see some of this in tomorrow’s post. Here’s one last example:

    The way you factor is personal preference. Pick the one you like, or flip-flop. There’re no rules!

    Share your preference (or a different way) in the comments!

  • How to Check if a Number is Divisible by 3 or 9

    How to Check if a Number is Divisible by 3 or 9

    This is a trick that everyone should learn in the 3rd grade. If not, then at least by the 9th grade.

    If you’re in the dark on this one, no big deal. Now’s the time to learn. If you’re a parent – this trick will win you points like crazy. Especially if you get to it before the teacher does.

    So here’s how it works. For both 3 and 9, start by adding up the digits in the number. If the result is divisible by 3, then so’s the original number. If the result’s divisible also by 9, then… you guessed it… so’s the original number.

    If your result is way to big to tell, do it again. Check out the videos for both:

    Questions or comments? Leave them in the comment section below.

  • How to Use the Quadratic Formula to Never Factor Polynomials Again

    How to Use the Quadratic Formula to Never Factor Polynomials Again

    We learn to factor polynomials so we can solve for x. Stuff like

    3x2 + 2x – 1

    can be easily factored into

    (3x – 1)(x + 1)

    But some things aren’t so easy. And some things are just down right a pain in the bottom. Like this one:

    18x2 + 189x + 490

    “Just shoot me,” you might be thinking. But cool your jets, cowboy. Here’s the first tool you need to never factor polynomials again:

    I know – who wants to memorize that formula? But wait. If you use that one formula that you can memorize, you never have to factor polynomials again. Watch:

    So the factoring isn’t bad on that one, right? How about this one:

    And how about if you come across one of these. Wouldn’t it be nice to get rid of all guesswork:

    This has some disadvantages, of course. You see that there’s a lot more arithmetic. And there’s some things to look out for. But if you hate trial and error (like I do), then you might be willing to take the bad with that good.

    Whatcha think?