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# p1 equation watch

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1. Hi
I always get confused on questions like this: Say I reached this equation:

Y-(-3) = 2(x - (-5))

How do I multiply the brackets out and rearrange to make Y the subject. Do I keep the -5 to make -10, and -3 to become +3, or since -ve multiplied by -ve becomes +ve, do I take them to be +ve?
Hope that makes sense
Thanks
2. (Original post by rt6)
Hi
I always get confused on questions like this: Say I reached this equation:

Y-(-3) = 2(x - (-5))

How do I multiply the brackets out and rearrange to make Y the subject. Do I keep the -5 to make -10, and -3 to become +3, or since -ve multiplied by -ve becomes +ve, do I take them to be +ve?
Hope that makes sense
Thanks
You can appreciate that double negatives gives positives. When you have that equation: Y-(-3) = 2(x - (-5)) you can automatically spot two double negatives.

The - (-3) becomes + 3 and - (-5) becomes + 5. So we have

Y + 3 = 2(x + 5)
=> Y + 3 = 2x + 10
=> Y = 2x + (10 - 3)
=> Y = 2x + 7

Is that OK?

Euclid
3. (Original post by rt6)
Hi
I always get confused on questions like this: Say I reached this equation:

Y-(-3) = 2(x - (-5))

How do I multiply the brackets out and rearrange to make Y the subject. Do I keep the -5 to make -10, and -3 to become +3, or since -ve multiplied by -ve becomes +ve, do I take them to be +ve?
Hope that makes sense
Thanks
The way you have written it, makes it the following:

y-(-3)=y+3
x-(-5)=x+5
y+3=2(x+5)
so y=2x+10-3
so y=2x+7

y - (-3) = 2[x - (-5)]
y + 3 = 2(x + 5)

if you subtract a negative number, you are effectively adding that number. if I lose -3 apples, I gain 3. so in general,

a - (-b) = a + b

you can also say this using multiplication:

a - (-b) = a + (-1)(-b) = a + b
5. Thanks a lot. I always got confused on whether I should leave them as negatives, but obviously not .

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Updated: January 9, 2005
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