Equations and NegativesDate: 05/23/99 at 19:27:51 From: Bri Subject: Writing out equations The problem is 6(-N) = 3(N)+72. I already know that you subtract 3N from both sides, but how? How do you subtract a positive N from a -N? Thanks a bunch! -Bri Date: 05/24/99 at 12:28:47 From: Doctor Peterson Subject: Re: Writing out equations Hi, Bri. There are two things you have to be familiar with to do this problem: negative numbers and the distributive property. The first thing to do is to simplify the equation by removing the parentheses. The "6(-N)" can be written as "-6N" by thinking of it as 6 (-1 * N) and applying the associative property. Our equation then becomes -6N = 3N + 72 Now, as you say, you have to subtract 3N from both sides: -6N - 3N = 72 Now we can use the distributive property "in reverse"; but to make it clearer for you, we can first rewrite the negatives: (-6)*N + (-3)*N = 72 (-6 + -3)*N = 72 -9N = 72 Finally, we can divide both sides by -9: N = 72/(-9) = -72/9 = -8 Working with negatives like this can be a little tricky at first, but if you think of it this way it should become natural to you with practice. - Doctor Peterson, The Math Forum http://mathforum.org/dr.math/ |
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