# Evaluating Mathematical Expressions

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When evaluating mathematical expressions, substitute the given numbers for variables, and complete the functions of the equation. Learn to substitute numerals for variables to solve algebraic equations with help from a math teacher in this free video math lesson.

Part of the Video Series: Math Problems & History
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## Video Transcript

So how do you evaluate mathematical expressions? Sounds kind of tough doesn't it? Hi I'm Jimmy Chang and I have been teaching college mathematics for nine years now and I'm here to give you a glimpse as to how you do that. When they give you an expression and they want you to evaluate that they have to give you some numbers to kind of plug in their place so here is an example as to what it entails. Suppose you want to evaluate the expression x2 to y - 3x y2. Now that's an expression that sounds opposing enough but look at what they give you. They're telling you that x = -1 and y is =2. So that means that for every x that you see on this expression you plug in -1 and then for every y that you see you plug in 2. So that is exactly what we are going to do so check this out. You have x is -1 squared X y is 2 - 3 x X is -1 and Y is 2 so Y squared is 2 squared and what you do after that is basically evaluating the expressions using the order of operations here. So first off -1 squared is going to give you 1. I'm going to leave everything else the way it is until I get to the 2 squared. 2 squared you know is going to give you 4. Now after that we simply do the multiplication side of the evaluation so here we go. 1 X 2, you know that is 2. Now this is where we are going to be very very careful here. -3 X -1 is going to give you a positive 3 and then you are going to multiply that by 4. Now what is left to do is 3 X 4 which you know is 12 and notice I am carrying down the 2 but the only thing left to do is 2 12 gives you 14. Now again what has opened the gates is for them to tell you the numbers of what X and Y were. So evaluating mathematical expressions is pretty easy once they give you the numbers. So I'm Jimmy and this has been evaluating mathematical expressions.

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