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Differentiating Core 1

Simple question I know, but I seem to have forgotten how to differentiate! Any help with where I have gone wrong would be appreciated - my answer is different to book so I'm presuming it's incorrect.

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Reply 1

username1560589

\frac{d}{dx}x^n = nx^{n-1}

Reply 2

Bobjim12

When decreasing the power, you subtracted 1/3 rather than 1.

Reply 3

Chucklevisionary

If you use your third line: y = 3x^-1/3. Then with dy/dx you multiply x's coefficient by the power and then decrease the power by 1. So dy/dx = -x^-4/3 . I hope that helps (and is correct) :smile:

Reply 4

OL350

Original post by Bobjim12

When decreasing the power, you subtracted 1/3 rather than 1.

Book is giving answer as 1000...do you know where I have gone wrong?

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Reply 5

Bobjim12

Original post by OL350

Book is giving answer as 1000...do you know where I have gone wrong?

It should be cube root of x squared not (cube root x ) squared.

Reply 6

OL350

Original post by Bobjim12

It should be cube root of x squared not (cube root x ) squared.

not quite understanding what you mean. Could you show it on paper?

Reply 7

Bobjim12

ImageUploadedByTapatalk1428501163.681938.jpg

Original post by OL350

not quite understanding what you mean. Could you show it on paper?

Reply 8

OL350

Original post by Bobjim12

Isnt that exactly what I've done and it's wrong. The answer is 1000.

Reply 9

Bobjim12

Original post by OL350

Isnt that exactly what I've done and it's wrong. The answer is 1000.

No. You have done this: ImageUploadedByTapatalk1428501379.703209.jpg

Reply 10

OL350

Original post by Bobjim12

No. You have done this: ImageUploadedByTapatalk1428501379.703209.jpg

they are both giving the same answer on my calculator? Please could you go through entire question as both answers we are getting are completely wrong.

Reply 11

Bobjim12

Original post by OL350

they are both giving the same answer on my calculator? Please could you go through entire question as both answers we are getting are completely wrong.

Yes. They do. I apologise. Are you sure its -2/3? And not -3/2?

-3/2 would give the answer of 1000

Reply 12

OL350

Original post by Bobjim12

Yes. They do. I apologise. Are you sure its -2/3? And not -3/2?

-3/2 would give the answer of 1000

Yes it's -2/3.
I can only presume the book has got it wrong. Thanks for the help anyway!

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Reply 13

Bobjim12

Original post by OL350

Yes it's -2/3.
I can only presume the book has got it wrong. Thanks for the help anyway!

Sorry! I have horribly misinterpreted the question. This is what to do:

ImageUploadedByTapatalk1428501893.249587.jpg

Edit: i should be sqrting a million not a hundred thousand!

(edited 9 years ago)

Reply 14

OL350

Original post by Bobjim12

Sorry! I have horribly misinterpreted the question. This is what to do:

ImageUploadedByTapatalk1428501893.249587.jpg

Edit: i should be sqrting a million not a hundred thousand!

Can you explain. Third line down please? Why do they form a fraction together (what have you done)?

Reply 15

Bobjim12

Original post by OL350

Can you explain. Third line down please? Why do they form a fraction together (what have you done)?

I have multiplied both sides by 100 to eliminate the right side fraction. Then i multiplied both sides by 3root x sqrd to eliminate the left side fraction.