Maths Ocr 2016 C1

is a stretch parallel to x axis of scale factor 2
THE SAME AS
a stretch parallel to Y axis of 1/2?

No, not really. take the point (2,2) for instance:
a stretch parallel to the x-axis scale factor 2 would transform it to (4,2), f(1/2x)
a stretch parallel to Y-axis scale factor 1/2 would transform it to (2,1), 1/2f(x)

Reply 321

FluffyCommie

5

Original post by dsouza22neeson

Sorry i still don't understand cos i cant remember how the diagram looked, was 0,0 inside the circle?

I'll draw it out for you and then reply with a picture, and i'll try to explain that :smile:

Reply 322

blinin7

1

Original post by FluffyCommie

No, not really. take the point (2,2) for instance:
a stretch parallel to the x-axis scale factor 2 would transform it to (4,2), f(1/2x)
a stretch parallel to Y-axis scale factor 1/2 would transform it to (2,1), 1/2f(x)

Thanks for the reply.

Surely they have the same gradient though, which is was is important when stretching? - or is that irrelevant?

Trying to see if I can get anything out of those 3 marks. Was 50/50 over saying 1/2 to Y or 2 to X and went for X instead...

Reply 323

LThomas694

2

Original post by ellie98

Hi everyone,
I personally found this paper very difficult and believe it was the hardest paper I have ever done out of all the spec questions and the Solomon papers too. Having looked through the unofficial markschemes I think I have lost about 20 marks. In my mock I got 69/72. Reassuringly, my maths teacher just sent round this email to my year:

I hope he is right about the grade boundaries.

That's really reassuring to know thank you! Grade boundaries are relative to how the whole population does so the top 80% get A etc. And it sounds like everyone found it really hard so I'm sure they'll reflect that. Just don't let it knock your confidence for C2! Also C1 in the past has had very high grade boundaries with a lot of people getting full marks whereas the grade boundaries for C2 are more normal so they might just have made C1 loads harder and kept C2 the same

Reply 324

duncant

2

Original post by FluffyCommie

I'll draw it out for you and then reply with a picture, and i'll try to explain that :smile:

https://gyazo.com/1b6eeb91cbb17834cd93d03e3222afd0

Reply 325

09brewh

3

well I'm utterly ****ed.

Reply 326

Logic4Life

17

Original post by 09brewh

well I'm utterly ****ed.

Trust me you have probably done better than you have thought mate. I have been feeling depressed the whole day after that exam but lets just pray for an easier c2 and s2 and lower grade boundaries. Don't let one exam dishearten you mate.

Reply 327

AnonUK21

Any ideas what the grade boundaries will be?

I got about 55 on that, which is terrible performance (~75%) compared to the 90ish%'s I was getting whilst doing past papers. Not sure if I just choked under pressure or if the exam was generally harder...

Reply 328

FluffyCommie

5

Original post by dsouza22neeson

Sorry i still don't understand cos i cant remember how the diagram looked, was 0,0 inside the circle?

As you can see from this terrible drawn diagram (Correct me if it's wrong):

The question asks you to find the range of values for r. I have labelled r in the diagram, and as it is labelled, would be the maximum radius for the smaller circle. Now, you know L (which i've labelled as the WHOLE dashed line) as the diameter, previously worked out as sqrt(45)
but to find the maximum value of r, we need to take the distance from the centre at (4,3) to the centre (0,0)
Using: L= ((x2-x1)^2 + (y2-y1)^2)^1/2 you calculate that L=5
Therefore, r = sqrt(45) - 5
and since r cannot be 0, we get the range 0<r<sqrt(45)-5 :smile:

Original post by duncant

https://gyazo.com/1b6eeb91cbb17834cd93d03e3222afd0

Where did you get y=2x-20 from. NOOO why did I get y=2x-5??

Reply 330

maxjackson5

2

Original post by DanMcGrathKB

Shut up max you're not road, posh boy

its a joke mate haha

Reply 331

Skipper12345

5

Original post by Dmitry_Mednov

It is wrong as if you use k as -5 or -6 it will not intersect the curve, I checked it at the end.

Actually, I think I was right as I tested it and sketched a graph... And also that's what they got on the unofficial mark scheme. https://docs.google.com/document/d/1GrOwL3hZzhJmn8rd9IyozRJX6e6-0fAlwbaEnJkJEnw/mobilebasic

Reply 332

FluffyCommie

5

Original post by duncant

https://gyazo.com/1b6eeb91cbb17834cd93d03e3222afd0

well, I just wasted 5 minutes of my life xD

Reply 333

Skipper12345

5

Hi, here is a link to an unofficial Mark scheme for today's paper! https://docs.google.com/document/d/1GrOwL3hZzhJmn8rd9IyozRJX6e6-0fAlwbaEnJkJEnw/mobilebasic

Reply 334

Logic4Life

17

Someone help me for the tangent question...
I worked out the coordinate of A which I got to be (10,0)
Then I used y1-y2/x1-x2 to get a gradient of -0.5. So the gradient of the tangent was 2.
Then use the Centre (4,3)
y-3=2(x-4)
y-3=2x-8
y=2x-5
WHAT DID I DO WRONG! :biggrin:

Reply 335

09brewh

3

Original post by Logic4Life

Someone help me for the tangent question...
I worked out the coordinate of A which I got to be (10,0)
Then I used y1-y2/x1-x2 to get a gradient of -0.5. So the gradient of the tangent was 2.
Then use the Centre (4,3)
y-3=2(x-4)
y-3=2x-8
y=2x-5
WHAT DID I DO WRONG! :biggrin:

You don't sub in the centre you sub in the coordinates at that point :/

Reply 336

FluffyCommie

5

Original post by blinin7

Thanks for the reply.

Surely they have the same gradient though, which is was is important when stretching? - or is that irrelevant?

Trying to see if I can get anything out of those 3 marks. Was 50/50 over saying 1/2 to Y or 2 to X and went for X instead...

What's more important with stretches, in C1 specifically, is just the transformation of specific points on the graph, as far as I know. So the gradient is irrelevant.

I'd also like to add that

Reply 337

Logic4Life

17

Original post by 09brewh

You don't sub in the centre you sub in the coordinates at that point :/

But I subbed in (10 0) for the second tangent on the next question!

Reply 338

iTomza

Original post by Luketidley

Circles also do not come up on C1, geometry of a circle is a topic on c2! The topics for C1 are;
Surds and Indices,
Quadratic functions, equations, graphs and transformations,
Coordinate geometry and straight lines,
Polynomials and the binomial expansion,
and Differentiation!

These are on my course and I'm doing WJEC.

This is for OCR