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So
now multiplying two numbers together is no big deal. |
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| 3
x 4 = 12 |
6
x 3 = 18 |
5
x 2 = 10 |
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But
what happens when one or both of the numbers are negative? |
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What
would you do with this puppy? |
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3
x - 4 = ?
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Here's
what happens. |
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First,
multiply the numbers together. |
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We're
multiplying a three and a four together, |
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so
we're going to get twelve. |
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The
real question is: is it a + 12 or a - 12? |
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What
does that - in front of the 4 do? |
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The
minus goes with the 4. |
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It's
called its sign. |
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A
number can have one of two different signs, |
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positive
+ or negative -. |
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We
have a special rule that says |
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if
the sign of a number is not written, it's positive. |
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That
means the 3 has an invisible plus sign. |
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The
3 is positive and the 4 is negative. |
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Enough
already here's how it works:
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When
we multiply two numbers together, |
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if
the signs are different the answer is negative. |
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If
the signs are the same, |
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either
both positive OR BOTH NEGATIVE, |
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then
the answer is POSITIVE. |
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Read
that again, especially the last part. |
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WHEN
WE MULTIPLY, |
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IF
BOTH SIGNS ARE NEGATIVE THE ANSWER IS POSITIVE. |
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SIGNS
DIFFERENT THE ANSWER IS NEGATIVE
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SIGNS
THE SAME THE ANSWER IS POSITIVE
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Examples: |
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5
x - 3 = - 15 |
Different
signs
makes the answer negative |
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-
6 x 2 = - 12 |
Different
signs
makes the answer negative |
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-
3 x - 4 = 12 |
Same
signs
makes the answer positive |
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copyright 2005 Bruce Kirkpatrick |
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