Algebra: Evaluating Expressions

Evaluating Expressions

I've used the word "evaluate" a lot so far, and as you've probably already figured out from context clues, it's just a fancy word for "give me the numeric answer."

Example 7: Evaluate the expression -2x2y if x = 4 and y = -3.

Solution: Since you know the values of x and y, replace (substitute) the variables with the corresponding number. I usually use parentheses to surround numbers I substitute in, to make sure I don't screw up the signs.

  • -2(4)2(-3)

Now, just apply the order of operations.

  • -2(16)(-3) = (-32)(-3) = 96
You've Got Problems

Problem 7: Evaluate the expression x(y - 3)2 if x = 5 and y = -1.

CIG Algebra

Excerpted from The Complete Idiot's Guide to Algebra 2004 by W. Michael Kelley. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.

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