Substituting Values Into an Algebraic Expression

Video Transcript

"How do you substitute values into an algebraic expression? That seems rather ugly. Hi, I'm Jimmy, and we're here to make substituting values into algebraic expressions incredibly straightforward for you. Now, at first, when you see an expression, it's not the prettiest in the world, but when you really think about it, when they give you numbers ahead of time, it actually make things a lot easier for you. So here's a little case in point. Suppose you have the expression 3x squared plus 4xy minus y. Well, it seems kind of rough at first, but they're telling you, let x be two, and y be negative one. So the idea here is for every x, you put two in, and then for every y, you put negative one in. So here's how it should be written. X, you know it to be two, so you're going to put the two in there. And keep everything else the same. So keep the three, keep the square. Plus four times...you know x is equal to two, and you know y is equal to negative one. You notice I'm putting parentheses there to kind of help separate the numbers a little bit better. Minus, and then the y, you know is negative one. Now, you let your operations do the job for you. The important thing is as long as you know the order of operations, you're going to be okay. Two to the second power, that's going to be four. Plus four times two is going to be eight. Times negative one is going to be negative eight. And negative and a negative's going to give you positive. So you really have plus one. Three times four, you know that to be 12. Plus negative eight plus one. To do the rest is pretty much history in that, like I said, you let the operations do the work for you because 12 plus negative eight is going to give you four. And the last thing to do is to add the one, and you and I both know what four plus one happens to be, and that's going to give you five. So an algebraic expression seems imposing at first, but if they give you numbers ahead of time, just let the operations do the job, as long as you plug them in the right place. I'm Jimmy, and that's how you substitute values into an algebraic expression."