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Mathematics 15 Online
OpenStudy (saifoo.khan):

Derivation problem.

OpenStudy (saifoo.khan):

\[\Large \sqrt{\frac{2x}{x-1}}\]

OpenStudy (saifoo.khan):

Asalam o alaikum @asnaseer bhai. :)

OpenStudy (asnaseer):

Salaam to you too saifoo! :) just rewrite it as:\[\frac{(2x)^{1/2}}{(x-1)^{1/2}}\]and use the quotient or product rule. see here: http://www.mathsrevision.net/alevel/pages.php?page=25

OpenStudy (saifoo.khan):

Can you please check where i'm going wrong?

OpenStudy (asnaseer):

will do - but for future ref if you save your images as .png format they will be a lot smaller and load quicker.

OpenStudy (saifoo.khan):

Alright, sure. Will try my best. Thanks.

OpenStudy (asnaseer):

your calculations up to u, u', v and v' look correct - but I cannot follow the rest - does it continue at the top right of the image?

OpenStudy (saifoo.khan):

Yes sir.

OpenStudy (saifoo.khan):

From right top.

OpenStudy (asnaseer):

you have v^2 incorrect in the denominator at the top right

OpenStudy (asnaseer):

no - sorry - ignore that - I misread....

OpenStudy (saifoo.khan):

\[(\sqrt{x-1})^2 = x-1\]I took it directly. Is that still wrong?

OpenStudy (asnaseer):

3rd step from top right looks wrong

OpenStudy (asnaseer):

the 1st term in the numerator in incorrect

OpenStudy (saifoo.khan):

Where i took LCM? Can you please correct it?

OpenStudy (asnaseer):

should be: \(\sqrt{x-1}\sqrt{x-1}\)

OpenStudy (saifoo.khan):

Oh! Right right!!! Thanks. Let me correct it then i'll show you!

OpenStudy (asnaseer):

ok - good luck! :)

OpenStudy (saifoo.khan):

Should the final answer be: \[-\frac{\sqrt 2}{2x-1 \sqrt{x^2 - x}}\]

OpenStudy (asnaseer):

doesn't look right

OpenStudy (saifoo.khan):

Because after correcting the mistake we get: \[\frac{x-1-x}{2\sqrt{x^2-x}} \times \frac{1}{x-1}\]

OpenStudy (saifoo.khan):

And we had sqrt 2 from the beginning of the problem.

OpenStudy (asnaseer):

in the denominator there do you mean:\[2(x-1)\sqrt{x^2-x}\]

OpenStudy (saifoo.khan):

YES YES! Missed that 2. Sorry.

OpenStudy (asnaseer):

then yes - I believe it is correct :) although you can also use wolframalpha to check your result: http://www.wolframalpha.com/input/?i=d%2Fdx+sqrt%282x%2F%28x-1%29%29

OpenStudy (saifoo.khan):

Yes! This is something which is confusing me. They have sqrt 2 in the denominator.

OpenStudy (asnaseer):

look near the bottom where it says: Alternate form assuming x>0

OpenStudy (asnaseer):

remember:\[\frac{\sqrt{2}}{2}=\frac{1}{\sqrt{2}}\]

OpenStudy (saifoo.khan):

OMG! Perfect! Got it! Thanks a ton! :)

OpenStudy (asnaseer):

yw :)

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