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Explain this surds answer

Can anyone explain what's going on here?

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Reply 1

Original post
by The_Architect
Can anyone explain what's going on here?

we can't see it

Reply 2

Adding the image after the fact because this website is so *****ily designed it hides 90% of post functionality until after you've posted:

Screenshot 2025-05-27 at 16-57-52 MathsWatch.png

Specifically 11(5+sqrt(3))/22 on the last line - shouldn't it be 11/22 to end up with the final solution? Why are we suddenly doing 22/11?

Reply 3

Original post
by The_Architect
Adding the image after the fact because this website is so *****ily designed it hides 90% of post functionality until after you've posted:
Screenshot 2025-05-27 at 16-57-52 MathsWatch.png
Specifically 11(5+sqrt(3))/22 on the last line - shouldn't it be 11/22 to end up with the final solution? Why are we suddenly doing 22/11?

So they've just done 2 steps in 1.
First they multiplied out 11(5+root3) to make 55 + 11root3
Then they divided everything by 11 to get (5 + root3) /2

Reply 4

Original post
by The_Architect
Adding the image after the fact because this website is so *****ily designed it hides 90% of post functionality until after you've posted:
Screenshot 2025-05-27 at 16-57-52 MathsWatch.png
Specifically 11(5+sqrt(3))/22 on the last line - shouldn't it be 11/22 to end up with the final solution? Why are we suddenly doing 22/11?

Simplest form means we need to divide the numerator and denominator by their HCF which is 11 in this case.

Reply 5

Original post
by isaac123444566
So they've just done 2 steps in 1.
First they multiplied out 11(5+root3) to make 55 + 11root3
Then they divided everything by 11 to get (5 + root3) /2

Why would you multiply out a bracket when we are simplying?

Reply 6

Original post
by Muttley79
Why would you multiply out a bracket when we are simplying?

Oh yeah sorry missed that, but technically its still the correct method nvm

Reply 7

Original post
by Muttley79
Simplest form means we need to divide the numerator and denominator by their HCF which is 11 in this case.

Thank you, this wasn't mentioned at all in the rest of the video, it just said to divide the coefficient by the denominator, which here would result in 0.5. MathsWatch is fine for everything else but there's a huge drop in quality and explanations for the grade 8/9 content.

Reply 8

Screenshot 2025-05-27 at 18-16-13 MathsWatch.png

Can anyone explain this one? Specifically why/how -2 sqrt(4) sqrt(2) on the third becomes -4 sqrt(2) on the fourth line? I get that the sqrt(4) becomes 2 but apart from that it makes no sense to me. If we're multiplying the -2 coefficient by 2 and sqrt(2), why do we do this randomly here when nothing else is being multiplied and we've already multiplied out the brackets earlier?

Reply 9

Original post
by The_Architect
Screenshot 2025-05-27 at 18-16-13 MathsWatch.png
Can anyone explain this one? Specifically why/how -2 sqrt(4) sqrt(2) on the third becomes -4 sqrt(2) on the fourth line? I get that the sqrt(4) becomes 2 but apart from that it makes no sense to me. If we're multiplying the -2 coefficient by 2 and sqrt(2), why do we do this randomly here when nothing else is being multiplied and we've already multiplied out the brackets earlier?
I mean thats just how it simplifies, because otherwise you wouldn't be able to only have root 2s and numbers, you would have a root 4 which is not the format the question wants

Reply 10

Original post
by isaac123444566
I mean thats just how it simplifies, because otherwise you wouldn't be able to only have root 2s and numbers, you would have a root 4 which is not the format the question wants

So -2 + 2(sqrt(2)) simplifies to -4 sqrt(2)? This doesn't seem right
(edited 7 months ago)

Reply 11

Original post
by The_Architect
So `-2 + 2(sqrt(2))` simplifies to `-4 sqrt(2)`?
Well its (-2)(2)(sqrt2), but your right

Reply 12

Original post
by The_Architect
So -2 + 2(sqrt(2)) simplifies to -4 sqrt(2)? This doesn't seem right

No because its not -2 + 2 (sqrt 2), its -2 x 2 (sqrt 2)

Reply 13

Okay so you're saying it's multiplication and not simplification. In that case my original question of why are we arbitrarily choosing to multiply here? How would you know when to do this? Is it just when there's 3 terms together like this?

Reply 14

Original post
by isaac123444566
We are arbitrarily choosing to multiply here because we want to remove all of the root 4s because the question wants the answer in the format 4 + root2 /14, do you want me to give u like a 5 min tutoring session to explain this its kinda hard over text

Tht is not allowed - you are not to offer tutoring.

Reply 15

Original post
by Muttley79
Tht is not allowed - you are not to offer tutoring.

ok just trying to help

Reply 16

Original post
by isaac123444566
We are arbitrarily choosing to multiply here because we want to remove all of the root 4s because the question wants the answer in the format 4 + root2 /14, do you want me to give u like a 5 min tutoring session to explain this its kinda hard over text

Nah it kind of makes sense now that I know what's happening and when I should be doing it, plus I have too much ground to cover before the next exam and should move on from surds already, and hope to god they don't come up on the next exam 😂 Thanks for your help I appreciate it

Reply 17

Original post
by The_Architect
Nah it kind of makes sense now that I know what's happening and when I should be doing it, plus I have too much ground to cover before the next exam and should move on from surds already, and hope to god they don't come up on the next exam 😂 Thanks for your help I appreciate it

No worries bro, u doing gcses asw?

Reply 18

Original post
by The_Architect
Screenshot 2025-05-27 at 18-16-13 MathsWatch.png
Can anyone explain this one? Specifically why/how -2 sqrt(4) sqrt(2) on the third becomes -4 sqrt(2) on the fourth line? I get that the sqrt(4) becomes 2 but apart from that it makes no sense to me. If we're multiplying the -2 coefficient by 2 and sqrt(2), why do we do this randomly here when nothing else is being multiplied and we've already multiplied out the brackets earlier?

We have the term 2 root 8 but we want to show everything as root two.

So we break 8 into 4 x 2 and so it becomes 2 (root 4 x root 2) and we know root 4 is 2

Does that help?

Reply 19

Original post
by Muttley79
We have the term 2 root 8 but we want to show everything as root two.
So we break 8 into 4 x 2 and so it becomes 2 (root 4 x root 2) and we know root 4 is 2
Does that help?

Bro I just said that and he said he understood u dont have to undermine my explanation by reiterating what i said 😭

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