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# Differentiate watch

1. (Original post by Malgorithm)
Be careful when differentiating with fractions. You have the first term correct, , but the rest of it is not quite right.

Try splitting up the fraction again like you did in Q1, so you get .

I did do that what have I done wrong
Simplifying the first equation, I got
4x^2 + 5x^-1 - 1

which differentiates to
8x-5x^-2
2. (Original post by Bevin)
I did do that what have I done wrong
Simplifying the first equation, I got
4x^2 + 5x^-1 - 1

which differentiates to
8x-5x^-2
You've done it right from what I can see.
Then you sub in your value of x (1)

To make life easier put it back so you have a positive index.

8x - (5/x²)

Which i'm pretty sure you did anyway

I'm just going to quickly work out B now and i'll get back to you.
3. (Original post by I_Like_Maths)
You've done it right from what I can see.
Then you sub in your value of x (1)

To make life easier put it back so you have a positive index.

8x - (5/x²)

Which i'm pretty sure you did anyway

I'm just going to quickly work out B now and i'll get back to you.

Okay thank you I actually put it in negatively, but that seems a lot easier!

Thank you so much for all this help, I didn't expect a response like this
4. (Original post by Bevin)
Okay thank you I actually put it in negatively, but that seems a lot easier!

Thank you so much for all this help, I didn't expect a response like this
No problem

For part b.

Once you then have the gradient just use the co-ordinates you obtained from part a and do what you mentioned previously and I think you should be ok from there

Let us know what you get
5. (Original post by I_Like_Maths)
No problem

For part b.

Once you then have the gradient just use the co-ordinates you obtained from part a and do what you mentioned previously and I think you should be ok from there

Let us know what you get
I got y=3x+5?
6. (Original post by Bevin)
I got y=3x+5?
I got slightly different. I'm not saying you're wrong cause i'm slightly rusty at the equation of the tangent but how did you get the 5?
7. (Original post by I_Like_Maths)
I got slightly different. I'm not saying you're wrong cause i'm slightly rusty at the equation of the tangent but how did you get the 5?
My workings out:

when x=1
y=8 -----> 4x1^2+4-2/1
therefore coordinates= (1,8)

At x=1, the gradient=3-----> 8x1-5/1 (from previous Q)

Equation---->
y-8=3(x-1)
y-8=3x-3
y=3x+5
8. (Original post by Bevin)
My workings out:

when x=1
y=8 -----> 4x1^2+4-2/1
therefore coordinates= (1,8)

At x=1, the gradient=3-----> 8x1-5/1 (from previous Q)

Equation---->
y-8=3(x-1)
y-8=3x-3
y=3x+5
I'm pretty sure that is right!
9. (Original post by Bevin)
My workings out:

when x=1
y=8 -----> 4x1^2+4-2/1
therefore coordinates= (1,8)

At x=1, the gradient=3-----> 8x1-5/1 (from previous Q)

Equation---->
y-8=3(x-1)
y-8=3x-3
y=3x+5
That looks fine to me. Apologies for my misleading advice XD i was kinda tired at the time. Did you manage to do the last part OK?
10. (Original post by Malgorithm)
That looks fine to me. Apologies for my misleading advice XD i was kinda tired at the time. Did you manage to do the last part OK?
(Original post by I_Like_Maths)
I'm pretty sure that is right!
It's quite alright, I was tired myself aha!
Thank you both for the very useful help!
Be prepared for more forums created by me, The TSR is my only hope of passing AS Maths
11. (Original post by Bevin)
It's quite alright, I was tired myself aha!
Thank you both for the very useful help!
Be prepared for more forums created by me, The TSR is my only hope of passing AS Maths

And why is TSR your only hope of passing AS maths?
12. (Original post by I_Like_Maths)

And why is TSR your only hope of passing AS maths?
No it wasn't it had a few questions after it This was just revision questions because I have a mock in January coming up.

I had a very good teacher in maths at GCSE and she was the only that didn't give up on me. I was nearly put into foundation paper at GCSE but I refused and said I was doing the higher paper, and with lots of help and lots of revision I got an A. I got my timetable for my AS subjects, and I was disappointed I didn't have her for any of my maths lessons. I then found out she had actually left the school, and she was the only teacher in the maths department that was approachable. My teachers aren't very approachable and no where near as helpful as my old maths teacher.I dunno, my grades have slumped considerably in maths and I knew that if I had my old maths teacher I would be doing so much better, my best friend agrees also. (He also got an A when predicted a C)
I've been highly inconsistent in maths. Doing extremely well in homeworks and then doing okay in tests (C's) but also getting D's, E's and in one case I got a U, even though I revised.
13. (Original post by Bevin)
No it wasn't it had a few questions after it This was just revision questions because I have a mock in January coming up.

I had a very good teacher in maths at GCSE and she was the only that didn't give up on me. I was nearly put into foundation paper at GCSE but I refused and said I was doing the higher paper, and with lots of help and lots of revision I got an A. I got my timetable for my AS subjects, and I was disappointed I didn't have her for any of my maths lessons. I then found out she had actually left the school, and she was the only teacher in the maths department that was approachable. My teachers aren't very approachable and no where near as helpful as my old maths teacher.I dunno, my grades have slumped considerably in maths and I knew that if I had my old maths teacher I would be doing so much better, my best friend agrees also. (He also got an A when predicted a C)
I've been highly inconsistent in maths. Doing extremely well in homeworks and then doing okay in tests (C's) but also getting D's, E's and in one case I got a U, even though I revised.
I understand where you are coming from my background is very similar to yours in the sense of having an excellent teacher which you excel under.

You say you have been doing well in your homework but getting the occasional D/E/U in tests. The 2 things that spring to my mind are either you're Struggling under time constraints in class for the test or you're panicking once you getting into the test. If it's time constraints then this will just get better with more and more practise.

If you're really willing to put the effort in here's what I would personally advise. Use Examsolutions (It's brilliant) revise any topics you need and once you feel you have enough for the module do a full paper and see what you can get. He has full papers with video's on how to do each question so once you have completed the paper you can watch video's on any question you struggled with.

If you're still struggling then post any questions on here or you could even message me personally I'd be happy to try help you as long as it's not M1

But I guess it also depends on what grade you specifically want at the end of the year
14. (Original post by I_Like_Maths)
I understand where you are coming from my background is very similar to yours in the sense of having an excellent teacher which you excel under.

You say you have been doing well in your homework but getting the occasional D/E/U in tests. The 2 things that spring to my mind are either you're Struggling under time constraints in class for the test or you're panicking once you getting into the test. If it's time constraints then this will just get better with more and more practise.

If you're really willing to put the effort in here's what I would personally advise. Use Examsolutions (It's brilliant) revise any topics you need and once you feel you have enough for the module do a full paper and see what you can get. He has full papers with video's on how to do each question so once you have completed the paper you can watch video's on any question you struggled with.

If you're still struggling then post any questions on here or you could even message me personally I'd be happy to try help you as long as it's not M1

But I guess it also depends on what grade you specifically want at the end of the year
Thank you, I'll have a look on that website
I want to do as well as possible, but I will be dropping maths after AS so as long as I get a C I will be happy
I always do better on calculator papers as well, so hopefully when it comes to me doing C2, I will be a lot happier.
I shall private message you with any concerns, thank you.

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Updated: December 2, 2014
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