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I'd like to take maths seriously but I'm not that great at it, so I decided to learn at home. I know this is pretty basic, but as I said, I'm pretty bad at maths, haha.

The worksheet gives me this example:

$7 (9o + 7) = 63o + 49$

I completed this one myself:

$5 (3l + 7) = 15l + 21$

My question is, what do I do if the plus operator is replaced with substraction?

Example:

$-3 (6w - 2)$

Here's what I got, although I doubt it's correct: $-18 w - -1.5$


Thanks kindly for your help!

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It is far better to type $-18 w - (-1.5)$ than $-18 w - \, -1.5$ (-18 w - -1.5), because this last one is not a standard notation. –  Américo Tavares Jan 12 '13 at 19:18
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2 Answers

up vote 4 down vote accepted

For any $\;a,\,b\,:\;\;\; a - b = a + (-b).\;\;$

So for your last example, we can proceed as follows:

$$-3(6w - 2)\, = \,-3\,[\,6w + (-2)\,]\, =\,(-3)(6w) + (-3)(-2)\, = \,-18w + 6$$

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It's same, $-3(6w - 2) = (-3)(6w) + (-3)(-2) = -18w + 6$

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