a_level185
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https://prnt.sc/up26kj

please help. i dont care about the working out. just need answers to check against my teachers solutions which i think is wrong
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mqb2766
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(Original post by a_level185)
https://prnt.sc/up26kj

please help. i dont care about the working out. just need answers to check against my teachers solutions which i think is wrong
What was your teachers solutions? Why do you think they're wrong?
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a_level185
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(Original post by mqb2766)
What was your teachers solutions? Why do you think they're wrong?
(79/300)* root 3. Which I put into a calculator and is 0.45. The estimate for 3/root 10 is 0.95. This seems way too far apart
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nerak99
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True, 0.95 is a bad estimate for 79/300 root 3 but without the your working, no-one here can help you.
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a_level185
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(Original post by nerak99)
True, 0.95 is a bad estimate for 79/300 root 3 but without the your working, no-one here can help you.
I would much rather do someone’s question than go through their long tideous working out
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mqb2766
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(Original post by a_level185)
I would much rather do someone’s question than go through their long tideous working out
Why not post your attempt then? I got close to .95 for the first three x terms (up to and including cubic).
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a_level185
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okay i will. so you agree with my teacher?
(Original post by mqb2766)
Why not post your attempt then? I got close to .95 for the first three x terms (up to and including cubic).
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mqb2766
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(Original post by a_level185)
okay i will. so you agree with my teacher?
I don't really know what you've / your teacher has done so not sure who I agree with. Note the 0.95 is just from the series expansion with the sqrt(3) removed and x=3/40., I.e. It's sqrt(0.9).
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a_level185
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(Original post by mqb2766)
I don't really know what you've / your teacher has done so not sure who I agree with. Note the 0.95 is just from the series expansion with the sqrt(3) removed and x=3/40., I.e. It's sqrt(0.9).
Is there a way you can upload a picture please? I’m a visual learner and reading this looks alien to me
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mqb2766
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(Original post by a_level185)
Is there a way you can upload a picture please? I’m a visual learner and reading this looks alien to me
Sorry, the aim is to help you come to an answer, not provide solutions.
Happy to help you with what you've done.
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a_level185
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https://prnt.sc/upgafu

im not the type of guy to expect others to do my homework for me. this isnt even my homework, it's past paper questions for my revision and i've tried relentlessly to get the answer but im out of hope.
i hope you can make sense of my work. i have tried to do it step by step
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mqb2766
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(Original post by a_level185)
https://prnt.sc/upgafu

im not the type of guy to expect others to do my homework for me. this isnt even my homework, it's past paper questions for my revision and i've tried relentlessly to get the answer but im out of hope.
i hope you can make sense of my work. i have tried to do it step by step
The series expansion part looks good, 759/800 which is sqrt(0.9) or 3/sqrt(10).
It's almost like there's an unnecessary sqrt (3) kicking around?
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a_level185
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(Original post by mqb2766)
The series expansion part looks good, 759/800 which is sqrt(0.9) or 3/sqrt(10).
It's almost like there's an unnecessary sqrt (3) kicking around?
https://prnt.sc/upgomb

im so confused, i did the other expansion and i got the same answer.... what do you mean by a square root hanging around?

i needed to multiply by 1/root 3 to get from 3root30/10 to 3/root 10 as the question asks.

oh wait i know what you mean about the root3. the question asks in the form kroot3. i dont know how to do that. so i thought id bring a root 3 out. but then k isnt a rational number
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mqb2766
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(Original post by a_level185)
https://prnt.sc/upgomb

im so confused, i did the other expansion and i got the same answer...
In your working you want to approximate 3sqrt(30)/10? Is that right?
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a_level185
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(Original post by mqb2766)
In your working you want to approximate 3sqrt(30)/10? Is that right?
yes. i expanded (3-4x)^1/2 . then when i sub in the given x value 3/40 , i get the approximation for 3sqrt(30)/10. so to find 3/root10, i multiplied everything by 1/root3.
thats how you get from 3root30/10 to 3/root10
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a_level185
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(Original post by mqb2766)
In your working you want to approximate 3sqrt(30)/10? Is that right?
the question is https://prnt.sc/upgtuz
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mqb2766
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(Original post by a_level185)
yes. i expanded (3-4x)^1/2 . then when i sub in the given x value 3/40 , i get the approximation for 3sqrt(30)/10. so to find 3/root10, i multiplied everything by 1/root3.
thats how you get from 3root30/10 to 3/root10
Ok that's different from the original question, but consistent with the answer. 759/800 = k is correct.

3/sqrt(10) = sqrt(9/10) = 759/800
3sqrt(30)/10 = sqrt(3) sqrt(9/10) = 759/800 sqrt(3)

3sqrt(30)/10 = 3sqrt(3)/sqrt(10)

Pick whichever answer is correct for the question.
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the bear
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there does not seem to be a √3 in the answer... it looks like the question is wrong.
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a_level185
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if k is 759/800 then thats like saying 3/root10 is (759/800)*root3. which is the estimation for (3root30)/10. not the estimation for 3/root10.

to get from (3root30)/10 to 3/root10, i need to multiply by 1/root3.

so then that is (759/800)*root3) multiplied by (1/root3.). so the root3 cancels out and the final answer is just 759/800. which isnt in terms of root 3.
and when you do 3/40 you get 0.94868. and 759/800 is o.94875. so that means that is the correct estimation because it's so close. But literally no way of making it in terms of root 3
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mqb2766
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(Original post by a_level185)
if k is 759/800 then thats like saying 3/root10 is (759/800)*root3. which is the estimation for (3root30)/10. not the estimation for 3/root10.

to get from (3root30)/10 to 3/root10, i need to multiply by 1/root3.

so then that is (759/800)*root3) multiplied by (1/root3.). so the root3 cancels out and the final answer is just 759/800. which isnt in terms of root 3.
and when you do 3/40 you get 0.94868. and 759/800 is o.94875. so that means that is the correct estimation because it's so close. But literally no way of making it in terms of root 3
No.
3/sqrt(10) = 759/800.
3 sqrt(3)/sqrt(10) = 3 sqrt(30/10 = 759/800 sqrt(3)
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