OCR MEI C2 MAY 18th

Original post by GreenLantern1

Of course they do! You are plottting the same thing!

Um, actually while y = -sin(x) and y = sin(-x) are equivalent, y = -cos(x) is not the same as y = cos(-x), in fact they are actually reflections of one another.

for example, take x = 0, y = -cos(x) = -cos(0) = -1
... but, y = cos(-x) = cos(0) = 1, not -1

Reply 62

Original post by skibur

Good luck everyone, lets hope you don't get a stinker of an exam like I did this time last year.

I hope we don't get a super hard one!
Thanks for the luck! Good luck with your A2s :smile:

Reply 63

Feeling a little bored, so does anyone have any quick maths questions on C2 they want answering :wink:

Reply 64

Original post by darbyj

Feeling a little bored, so does anyone have any quick maths questions on C2 they want answering :wink:

Could you explain what first principles are?
I don't have a clue and maybe you could help :smile:

Reply 65

Original post by Alotties

Could you explain what first principles are?
I don't have a clue and maybe you could help :smile:

Sure, I'd like to help if I can :smile:

First principles is a proof used to show the principle of differentiation. In essence it is similar to the the idea that gradient is change in y over change in x.

For example; a first principle would be f(x+h) - f(x) all divided by x

Why?

Well, if you are taking a starting value of x as being x (in this example) and then moving a very small distance, h then your change in x will be h.

Equally, your change in y, will be the difference between f(x) and f(x+h).

The idea being that h will tend to zero, thus leaving you with the same result, as though you have differentiated normally.

Reply 66

ILM16

1

So who has yet to start revision?

Reply 67

Original post by darbyj

Sure, I'd like to help if I can :smile:

First principles is a proof used to show the principle of differentiation. In essence it is similar to the the idea that gradient is change in y over change in x.

For example; a first principle would be f(x+h) - f(x) all divided by x

Why?

Well, if you are taking a starting value of x as being x (in this example) and then moving a very small distance, h then your change in x will be h.

Equally, your change in y, will be the difference between f(x) and f(x+h).

The idea being that h will tend to zero, thus leaving you with the same result, as though you have differentiated normally.

Ohhh! I think I see.
I have done some of these questions I think but never knew they were first principles :tongue:

Thank you (+1 for your help) :smile:

Reply 68

That may not be very clear, so I am using the past paper from June 2009 to illustrate my point;

12 i) Calculate the gradient of the chord joining the points on the curve y = x² - 7 for which x = 3 and x = 3.1

gradient = ( f(3.1) - f(3) ) / (3.1 - 3) = 0.61/0.1 = 6.1

ii) Given that f(x) = x² - 7, find and simplify ( f(3+h) - f(3) ) / h

So substituting into the equation of the curve;

f(3 + h) = (3 + h)² - 7 and f(3) = 2

so ( f(3+h) - f(3) ) / h = (9 + 6h + h² - 7 - 2) / h = ( 6h + h² ) / h = 6 + h

Notice anything about this? If you were to differentiate y = x² - 7, and use that to find the gradient at x = 3, you would get the result 6. Well here you have got the result 6 + h, and if you take h as being very small (i.e. zero) then it is just 6.

I hope that helped!

(edited 11 years ago)

Reply 69

Original post by Alotties

Ohhh! I think I see.
I have done some of these questions I think but never knew they were first principles :tongue:

Thank you (+1 for your help) :smile:

Glad I could help :biggrin:

Reply 70

Original post by darbyj

Glad I could help :biggrin:

I understand it a lot better now hehe :biggrin:

If it comes up tomorrow I hope I remember what you've said xD

Reply 71

ILM16

1

I always forget, can someone remind me about this:

If log10 A = c, why does A = 10^c?

Reply 72

dongonaeatu

Original post by ILM16

I always forget, can someone remind me about this:

If log10 A = c, why does A = 10^c?

it just does ok

Reply 73

posting

Original post by ILM16

I always forget, can someone remind me about this:

If log10 A = c, why does A = 10^c?

Its just a rule of logs... I know its stupid :frown:

Reply 74

alex7892