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# C1 Maths Help: Surds - Where did I go wrong in this question? watch

1. 10/r5 + 4/r5-r7

10r5-10r7 + 4r5/r5(r5-r7)

14r5 – 10r7/5 – r35

(14r5 – 10r7)(5 + r5r7)

70r5 + 70r7 – 50r7– 70r5

20r7

Should be -2r7
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2. I can't follow this. If you write it up in LaTeX or upload an image I may be able to help you.
3. Do them seperatley then put them together. So do 10r3/r15 first to get 2r5. then do the second bit to get -2r5 -2r7.
put then together to get

2r5 - 2r5 - 2r7

the 2r5 and -2r5 cancel so you are left with -2r7

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4. Hope that helps

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5. (Original post by ImNervous)
Do them seperatley then put them together. So do 10r3/r15 first to get 2r5. then do the second bit to get -2r5 -2r7.
put then together to get

2r5 - 2r5 - 2r7

the 2r5 and -2r5 cancel so you are left with -2r7

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Ah thank you sooo much! You're fantastic!
6. No problem

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7. (Original post by creativebuzz)
10/r5 + 4/r5-r7

10r5-10r7 + 4r5/r5(r5-r7)

14r5 – 10r7/5 – r35

(14r5 – 10r7)(5 + r5r7)

70r5 + 70r7 – 50r7– 70r5

20r7

Should be -2r7
Multiply both sides by the second denominator over the second denominator but with a plus sign (it's pair)

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