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# OCR C4 (not mei) 18th June 2013 revision Watch

1. (Original post by h2shin)
Stationary points for the trig: (pi/2, 1) (pi/6, 1.5) (5pi/6, 1.5)
Any agreements?
yeah i got them apart from the first one.... oh well
2. (Original post by ihatepeople37)
when you had to integrate x^8 ln3x ... i put u as ln3x but what is that differentiated please???
its 3/3x .. f'(x)/f(x)
3. (Original post by 94Singh)
its 3/3x .. f'(x)/f(x)
yeah and when you simplify 3/3x it becomes 1/x
4. (Original post by eggfriedrice)
Pretty sure it was a maximum. You differentiate it again and find it's negative. (C1)
Yeah, I got maximum, too. d*2y/dx*2 was <0, which made it a maximum. I think.
5. that paper was messed up!!!!
6. (Original post by h2shin)
Stationary points for the trig: (pi/2, 1) (pi/6, 1.5) (5pi/6, 1.5)
Any agreements?

Oh and gradient to left was negative and gradient to right was positive so I put minimum but can't be too sure...
how did you get the first one?
7. (Original post by ihatepeople37)
yeah i got them apart from the first one.... oh well
I only got two stationary points, also! Was there another one?
8. for the stationary point question was t=-1?
9. ohhh **** just realized they had to be 3 stationary points I put 1
10. (Original post by eggfriedrice)
Pretty sure it was a maximum. You differentiate it again and find it's negative. (C1)
Just plotted the function. It was a minimum.
11. (Original post by Dizzy in my Head)
Yeah, I got maximum, too. d*2y/dx*2 was <0, which made it a maximum. I think.
but it said by considering the gradient either side
12. (Original post by louise_234)
yeah and when you simplify 3/3x it becomes 1/x
but 1/x is integrated it is lnx not ln3x, or am i being really stupid??
13. So much volume!
14. (Original post by a10)
ohhh **** just realized they had to be 3 stationary points I put 1
Thats what I got as well :/ fml
15. Okay I'm petrified now, you guys all seemed to find it alright!

I can't be the only one who thought it was horrific?
16. (Original post by louise_234)
yeah and when you simplify 3/3x it becomes 1/x
yeah .. they differentiate to become the same .. try putting them into your calculator if you have one that can differentiate
17. This is effectively a preliminary markscheme until Mr M posts his full definitive solutions. Some of my answers may be wrong. Spoilered incase you don't want to see them

*A few additions have been made to the markscheme* - namely the cartesian equation (forgot to put it in)

Spoiler:
Show
1.

2.

3. Skew. Solved the first two equations for and and then substituted into the third equation for 18=-38 which is clearly untrue, thus the equations are inconsistent and the lines are skew.

4.

Stationary points are

5.

Integral was

6.

7.

Angle BAC = 171.3 degrees (1 d.p.)

Show that AD is perpendicular to AB and AC by finding the dot product of AD and AB, and then AD and AC - and showing that both dot products equate to 0.

I messed up on the volume of the pyramid

8.

Letting t=0, finding r and substituting gives V = 30.5 cm^3 (3 s.f.)

9.

Solving dy/dx yields t=1 which corresponds to the point (0,3)

When t>1 x<0 and dy/dx is negative
When t<1 x>0 and dy/dx is positive

Hence it is a minimum

Cartesian equation...

10. Show.

Let x=0.1 for 0.136

Same substitution would be unsuitable as the expansion here is valid for which is the same as
18. (Original post by Maid Marian)
Okay I'm petrified now, you guys all seemed to find it alright!

I can't be the only one who thought it was horrific?
Dont worry, so did I and most of my year. Just realised marks here and there missed too
19. (Original post by Maid Marian)
Okay I'm petrified now, you guys all seemed to find it alright!

I can't be the only one who thought it was horrific?
No. I agree. I thought is was dreadful. I'm so angry with myself! I can't wait for someone to post an unofficial mark scheme.
20. I got t=1 and two stationary points ._.

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