Math Is Fun Forum

silverpuma

Member

Registered: 2011-06-19

Posts: 80

Diff / equation of curve / perp problem. I can't get the textbook answ

Hi, as an old codger I'm working my way through GCSE further maths textbook, self teaching myself to help my son.  The last section on Tangent and Normal have 10 questions and I have 8 of them finished and correct but these 2 I have checked and rechecked but still am making a mistake somewhere as my answer and the textbook are not the same.

No doubt it will be an embarrassingly easy fix but.....I can't see it, my 1.5 brain cells are overheating......help:-)

question and my workings

Thanks guys for any and all help.........

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“Men occasionally stumble over the truth, but most of them pick themselves up and hurry off as if nothing ever happened.”  ―  Winston Churchill

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Diff / equation of curve / perp problem. I can't get the textbook answ

How did you get from:

to:

?

Last edited by anonimnystefy (2015-07-11 02:59:32)

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“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

silverpuma

Member

Registered: 2011-06-19

Posts: 80

Re: Diff / equation of curve / perp problem. I can't get the textbook answ

I multiplied by -4 to clear the Denominator of the fraction and to make the power of the other term positive, should I not have done this?

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“Men occasionally stumble over the truth, but most of them pick themselves up and hurry off as if nothing ever happened.”  ―  Winston Churchill

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Diff / equation of curve / perp problem. I can't get the textbook answ

But, multiplying by (-4) does not change the power of x there.

---

“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

silverpuma

Member

Registered: 2011-06-19

Posts: 80

Re: Diff / equation of curve / perp problem. I can't get the textbook answ

But, multiplying by (-4) does not change the power of x there.

aaaahh so thats part of my problem in both questions, thanks for that, but I'm a bit stuck how to work with the negative power.

I get it now and your prompting made the difference....yipppeeeee   Something for me to be very careful with moving forward

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“Men occasionally stumble over the truth, but most of them pick themselves up and hurry off as if nothing ever happened.”  ―  Winston Churchill

silverpuma

Member

Registered: 2011-06-19

Posts: 80

Re: Diff / equation of curve / perp problem. I can't get the textbook answ

I realised after I said I had it sorted I still wasn't right so after a bit of head scratching I think I understand my mistake and the long journey getting to grips with it was worthwhile. 

But......just in case I wonder would you have another look at my new working out especially the area inside the black box on top right side of page as this was where my trouble was.  I'd be really grateful if you could be critical as I want to kelp doing this the "best" or most efficient way I can and not be sloppy in my working out method, so be ruthless;-)  It still seems to be that they is probably a more elegant way.

new workings

Thanks again........

Last edited by silverpuma (2015-07-11 06:07:26)

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“Men occasionally stumble over the truth, but most of them pick themselves up and hurry off as if nothing ever happened.”  ―  Winston Churchill

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Diff / equation of curve / perp problem. I can't get the textbook answ

Hi;

That link is not coming in.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

silverpuma

Member

Registered: 2011-06-19

Posts: 80

Re: Diff / equation of curve / perp problem. I can't get the textbook answ

Hi;

That link is not coming in.

http://1drv.ms/1IRK0b9

Try to copy and paste this into your browser thanks...........

I'll try again at the link  http://1drv.ms/1IRK0b9

Last edited by silverpuma (2015-07-11 23:25:01)

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“Men occasionally stumble over the truth, but most of them pick themselves up and hurry off as if nothing ever happened.”  ―  Winston Churchill

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Diff / equation of curve / perp problem. I can't get the textbook answ

Hi;

Still can not get it.

Does anyone else see it?

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

silverpuma

Member

Registered: 2011-06-19

Posts: 80

Re: Diff / equation of curve / perp problem. I can't get the textbook answ

Hi;

Still can not get it.

Does anyone else see it?

It works for me both ways in browser and link?  Maybe that's because its on my computer etc, don't know?

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“Men occasionally stumble over the truth, but most of them pick themselves up and hurry off as if nothing ever happened.”  ―  Winston Churchill

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Diff / equation of curve / perp problem. I can't get the textbook answ

Might be mine, maybe some one else can see it.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

silverpuma

Member

Registered: 2011-06-19

Posts: 80

Re: Diff / equation of curve / perp problem. I can't get the textbook answ

ok thanks bobbym

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“Men occasionally stumble over the truth, but most of them pick themselves up and hurry off as if nothing ever happened.”  ―  Winston Churchill

silverpuma

Member

Registered: 2011-06-19

Posts: 80

Re: Diff / equation of curve / perp problem. I can't get the textbook answ

The links that you cant see are using onenote so this time I have used a link to my dropbox account to see if it will work there

https://www.dropbox.com/s/oma5638hr15wgrr/new-work.jpg?dl=0

try this

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“Men occasionally stumble over the truth, but most of them pick themselves up and hurry off as if nothing ever happened.”  ―  Winston Churchill

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Diff / equation of curve / perp problem. I can't get the textbook answ

I think you need a account there to see that.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Diff / equation of curve / perp problem. I can't get the textbook answ

---

“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.