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# C1 question help watch

1. I'm not sure how I would do question 11? I've tried but I am getting a wrong answer. Any help?

http://crashmaths.com/wp-content/upl...0/C1SETBQP.pdf

x
2. (Original post by needsomehelpnow)
I'm not sure how I would do question 11? I've tried but I am getting a wrong answer. Any help?

http://crashmaths.com/wp-content/upl...0/C1SETBQP.pdf

x
What have you tried?
3. (Original post by SeanFM)
What have you tried?
Nothing really. I know how to do it when there is f'(x) and one point, but not f''(x) and two points :/

I don't know where to start
4. (Original post by needsomehelpnow)
Nothing really. I know how to do it when there is f'(x) and one point, but not f''(x) and two points :/

I don't know where to start
How do you get to f'(x)?

And from there, how do you get to f(x)?
5. (Original post by SeanFM)
How do you get to f'(x)?

And from there, how do you get to f(x)?
Integrate? That's what I did before, but got the wrong answer.

I integrated f''(x) to get f'(x). Then I subbed in my point to get c and then I integrated again. But it's not right
6. (Original post by needsomehelpnow)
Integrate? That's what I did before, but got the wrong answer.

I integrated f''(x) to get f'(x). Then I subbed in my point to get c and then I integrated again. But it's not right
You're aware that the x in the denominator can be cancelled by one of each of the three x's in the numerator? If so, then integrating it is really easy as you merely needed to integrate the individual expressions.
7. (Original post by multiratiunculae)
You're aware that the x in the denominator can be cancelled by one of each of the three x's in the numerator? If so, then integrating it is really easy as you merely needed to integrate the individual expressions.
I know that and I did that. My integral is right, but the constants are wrong.

I don't know why. I integrate to get f'(x) then substitute my point in to get the first constant. Then I integrate again for f(x) to get the second constant. But it's wrong??
8. (Original post by needsomehelpnow)
I know that and I did that. My integral is right, but the constants are wrong.

I don't know why. I integrate to get f'(x) then substitute my point in to get the first constant. Then I integrate again for f(x) to get the second constant. But it's wrong??
You integrate twice first! f'(x) is irrelevant here.
9. (Original post by multiratiunculae)
You integrate twice first! f'(x) is irrelevant here.
Why
10. (Original post by needsomehelpnow)
Integrate? That's what I did before, but got the wrong answer.

I integrated f''(x) to get f'(x). Then I subbed in my point to get c and then I integrated again. But it's not right
As someone else is helping I'll take my leave, but remember that you don't know what f'(x) is for either of those points, you just have two values of x and two corresponding values of f(x).
11. (Original post by needsomehelpnow)
Why
but remember that you don't know what f'(x) is for either of those points, you just have two values of x and two corresponding values of f(x).There you go.
12. I solved it.

c=-12.5
d=7.25
13. (Original post by multiratiunculae)
but remember that you don't know what f'(x) is for either of those points, you just have two values of x and two corresponding values of f(x).There you go.
Ohhhh, ok

So I get two simultaneous equations and I solve them

Could you help me with question 6? My teacher said it is an easy question but I can't get my head round it :/
14. (Original post by needsomehelpnow)
Ohhhh, ok

So I get two simultaneous equations and I solve them

Could you help me with question 6? My teacher said it is an easy question but I can't get my head round it :/
What's not to get?
15. (Original post by multiratiunculae)
What's not to get?
how I prove it's a rectangle...
16. (Original post by needsomehelpnow)
how I prove it's a rectangle...
Do you know what a rectangle is......
17. (Original post by multiratiunculae)
Do you know what a rectangle is......
Yes, there is no need to patronise me - I'm just confused.

I'm not sure if working out the gradients of the lines joining all the vertices and proving that they are perpendicular/parallel is a valid method. It seems like a bit too much for 5 marks... hence the confusion
18. (Original post by needsomehelpnow)
Yes, there is no need to patronise me - I'm just confused.

I'm not sure if working out the gradients of the lines joining all the vertices and proving that they are perpendicular/parallel is a valid method. It seems like a bit too much for 5 marks... hence the confusion
There are all sorts of methods. Why shouldn't that be valid. Supply a sketch too. You could prove that 4 right angles are formed, that the corresponding lines are equal in magnitude etc.

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