Rationalising the denominator question help

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username4434126
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#1
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#1
Need help with this question. So I am rationalising the denominator (removing any surds from the bottom). In this question as you can see in the picture, my answer is incorrect.

On my calculator it shows the answer as:

3 − √2
7

I am abit confused here, need help thanks
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username4434126
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#2
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#2
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Lala143
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#3
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#3
Sorry, I just edited out my latest comment because you can come to the same answer either way.
Last edited by Lala143; 3 years ago
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username4434126
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#4
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(Original post by Lala143)
Sorry, I just edited out my latest comment because you can come to the same answer either way.
I didn't see your previous comment so no problem. So my answer was correct? And why does it show different on the calculator? How did the negative at the denominator just disappear? That is where I am confused really. Want to thoroughly understand this before I move on
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Lala143
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#5
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#5
Yes I got the same answer as you and I don't know why the calculator seems to be getting that answer, maybe it multiplied by -1 but I don't know why. Sorry, I took a while to get back to you I had to do a bit of my own homework.
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username4434126
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#6
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(Original post by Lala143)
Yes I got the same answer as you and I don't know why the calculator seems to be getting that answer, maybe it multiplied by -1 but I don't know why. Sorry, I took a while to get back to you I had to do a bit of my own homework.
No problem. It not only says it on my calculator but also on my revision book under answers.

If anyone knows why its that answer and not mine do tell me, I really want to understand this.
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username4434126
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#7
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#7
I might have figured out why its that answer instead of mine. There are both minus signs on top and bottom so i assume they are being divided so the signs switch to positive as both have the same minus sign. Am I right?
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Lala143
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#8
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#8
I don't think so because you are not cancelling it any further but maybe I'm wrong.
(Original post by mannyman6)
I might have figured out why its that answer instead of mine. There are both minus signs on top and bottom so i assume they are being divided so the signs switch to positive as both have the same minus sign. Am I right?
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username4356336
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#9
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Your answer is correct but it's bad practice to write it like that.
Factorise the numerator: -(3-sqrt(2)), just flip the signs inside.
Then negative/negative = positive, so cancel the negative signs.

3-sqrt(2)/(7)
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username4434126
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#10
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#10
(Original post by sdr981)
Your answer is correct but it's bad practice to write it like that.
Factorise the numerator: -(3-sqrt(2)), just flip the signs inside.
Then negative/negative = positive, so cancel the negative signs.

3-sqrt(2)/(7)
This was helpful, thank you!
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the bear
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#11
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#11
your answer is equivalent to the book answer.

you will not lose marks if you have a version with lots of minuses.
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