Oh this bloody quotient rule - HELP!

Hi all,

I would appreciate if someone could solve this problem for me.

I got it from the textbook, so I have the answer, but I can't get how to arrive to it.

Please upload the solution in word, pdf or jpg format (via paint or photoshop)

Much obliged.

I hate my maths revision.

(edited 13 years ago)

Original post by the_13th

Hi all,

I would appreciate if someone could solve this problem for me.

I got it from the textbook, so I have the answer, but I can't get how to arrive to it.

Please upload the solution in word, pdf or jpg format (via paint or photoshop)

Much obliged.

I hate my maths revision.

I see no problem? ...

Edit: Ah I see it now.

Edit 2: Scratch all of that.

(edited 13 years ago)

Reply 2

dknt

12

Original post by the_13th

Hi all,

I would appreciate if someone could solve this problem for me.

I got it from the textbook, so I have the answer, but I can't get how to arrive to it.

Please upload the solution in word, pdf or jpg format (via paint or photoshop)

Much obliged.

I hate my maths revision.

Well post your working and we will see where you've gone wrong.

Reply 3

the_13th

OP

Original post by laughylolly

I see no problem? ...

Edit: Ah I see it now.

You can simplify the rest....

What is the answer in the text book? I think my method is right...

Hmmm... doesn't look like that.

That's the textbook's answer/

mamama2.JPG9.0KB

Reply 4

the_13th

OP

Original post by laughylolly

I see no problem? ...

Edit: Ah I see it now.

You can simplify the rest....

What is the answer in the text book? I think my method is right...

I think we must use quotient rule since the question says "using quotient rule find dy/dx"

Reply 5

TheDustyKid

15

Don't you have to divide by 'v^2' for quotient rule...?

Reply 6

the_13th

OP

Original post by laughylolly

Working above ^ ^ don't know if you have seen it.

My simplified answer is :

- \frac{2x + 1/2}{\sqrt[2]{(2x+5)(x-3)^{3}}}

This could be completely wrong though...

I can't judge really.

I have tried to solve this probelm 3 times and I get a different answer every time (but never the right one).

The answer from the textbook is in my previous message - check it.

Reply 7

the_13th

OP

Original post by TheDustyKid

Don't you have to divide by 'v^2' for quotient rule...?

yes, you do. I still get wrong answers.

Reply 8

dknt

12

Original post by laughylolly

I see no problem? ...

Edit: Ah I see it now.

You can simplify the rest....

What is the answer in the text book? I think my method is right...

You've gone wrong in your second line. You can't multiply the brackets like that, if you've got the power of -1 in there.

Reply 9

Pheylan

2y\dfrac{dy}{dx}=\dfrac{d}{dx}[(x-3)(2x+5)^{-1}]=(2x+5)^{-1}-2(x-3)(2x+5)^{-2}

Can you finish it off?

Reply 10

F1Addict

12

Just did it now on paper and the answer given in the book is right.

Reply 11

coldfusion

2

Original post by the_13th

Hi all,

I would appreciate if someone could solve this problem for me.

I got it from the textbook, so I have the answer, but I can't get how to arrive to it.

Please upload the solution in word, pdf or jpg format (via paint or photoshop)

Much obliged.

I hate my maths revision.

OK there is a lot of confusion here.

Start by distributing the square root into both the numerator and denominator so you end up with one nice fraction. Now apply the quotient rule.

Reply 12

StephenP91

3

I managed to get it out.

Reply 13

the_13th

OP

Original post by F1Addict

Just did it now on paper and the answer given in the book is right.

can you upload a picture of your paper with the solution? I'm stuck.

Reply 14

coldfusion

2

Original post by Pheylan

2y\dfrac{dy}{dx}=\dfrac{d}{dx}[(x-3)(2x+5)^{-1}]=(2x+5)^{-1}-2(x-3)(2x+5)^{-2}

Can you finish it off?

I forget, is implicit differentiation taught before or after quotient rule? Your method is much more elegant and is probably best for avoiding algebraic errors.

Reply 15

the_13th

OP

Original post by laughylolly

Scratch that. Sorry I've never done this rule before but I thought I would give it a go. Looked it up and I agree with the 11 on top from the textbook answer but on the bottom I got (2x+5)^2

Why the neg? Sorry for trying...

hahaha, it wasn't from me. Thanks for trying.

Reply 16

the_13th

OP

Original post by coldfusion

I forget, is implicit differentiation taught before or after quotient rule? Your method is much more elegant and is probably best for avoiding algebraic errors.