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# Edexcel C2 20th May 2015 *Official Thread* watch

1. How did you get log 64?
(Original post by ozzie2)
From the log rules, the left side can be rewritten as log4(a/b) and right can be written as log4(64)

Then you remove the logs so it is now a/b=64
x both sides by B so a=64b
Now sub a=64b into the first equation
64b(b)=25
64b^2=25
Root both sides
8b=5
b=5/8

Then sub in b=5/8 into the first equation
a(5/8)=25
a=40

Tell me if I am wrong but that's what I thought of doing
2. (Original post by Oz_Vessalius)
you only need to sort of understand what those graphs are but you dont need to remember them. its nice to have an idea of what they are but you dont need to; just remember how to use one solution to an equation to get the rest - ie. 2pi - theta for cos, pi - theta for sin, theta + 2pi for both of them and theta + pi for tan
For both cos and sin?Can i use this general formula instead of the cast diagram?
3. (Original post by ozzie2)
From the log rules, the left side can be rewritten as log4(a/b) and right can be written as log4(64)

Then you remove the logs so it is now a/b=64
x both sides by B so a=64b
Now sub a=64b into the first equation
64b(b)=25
64b^2=25
Root both sides
8b=5
b=5/8

Then sub in b=5/8 into the first equation
a(5/8)=25
a=40

Tell me if I am wrong but that's what I thought of doing

see what i did, is a= 25/b

then instead of a i wrote 25/b

as

log 25/b - log b = 3

and then, should i use the division rule over here? or subtract rule?

4. Edexcel have clarified that the paper hasn't been leaked. So stop asking if it's been leaked or not.
Attached Images

5. Hi I'm not sure how you can tell whether the estimate for the trapezium rule is an underestimate or an overestimate?
6. (Original post by 43zombiegit)
Anyone got a list of all of the formula's we need to know?
Volume of a cone, pyramid, sphere...
7. https://c4a3f001dcd45afe69d0ceec8300...%20Edexcel.pdfFor Q6) whenever they ask you if it's a diameter do you use that formula?And can you help me with: 6c, q8b and 9a

Also, for question 4c if it was an underestimate how would i have explained the reasoning?
8. (Original post by Elliemay97)
Hi I'm not sure how you can tell whether the estimate for the trapezium rule is an underestimate or an overestimate?
Pretend you are drawing a dot to dot on the graph, for each of the x values in the table. You will be able to tell whether it is an overestimate or underestimate based on what you've drawn on the graph - try it you might get it without any further explanation.
9. (Original post by Tizzydag)
Can somebody please explain what chapter 8, "graphs of trig. functions is all about" and what we need to know from that topic. do questions come up just on that one topic alone or are they mixed with trig identities?
thanks
Chapter 8 is pretty much preparing you for chapter 10. Just remember Cos^2 (x) + Sin^2 (x) = 1 as this is bound to come up for a proof question but there are usually big marks for solving the equations like tanx + sinx = 1 or something, try a few questions and reffer to the book and also remember

tanx = sinx/cosx
10. (Original post by Olon)
For both cos and sin?Can i use this general formula instead of the cast diagram?
Yeah you can. It's probably best if you understand why it works based on the graphs but you don't strictly need to.
So for inverse sine answers, you do 180deg/pi minus theta to get your second solution and then add 2pi to each of those to get the rest
And for inverse cosine answers, you do 360deg/2pi minus theta to get your second solution and then add 2pi to each of those to get the rest.
Then for inverse tan solutions you just keep adding 180deg/pi.

CAST diagram has always confuse me too. If you are unsure your answers are correct always just plug them back into sin cos or tan functions and double check.

(Original post by Elliemay97)
Hi I'm not sure how you can tell whether the estimate for the trapezium rule is an underestimate or an overestimate?
(Original post by El-Presidente)
Pretend you are drawing a dot to dot on the graph, for each of the x values in the table. You will be able to tell whether it is an overestimate or underestimate based on what you've drawn on the graph - try it you might get it without any further explanation.
Yeah, you can always just draw the trapeziums that you are working out the area of and see for yourself whether you've got yourself an overestimate or an underestimate
11. (Original post by userxx990)
How did you get log 64?
Well everything else is in log4 so you want to get the 3 in the same form to remove the logs and 4^3 is 64, so log4(64) = 3 therefore you can change the 3 to log 64

(Original post by userxx990)

see what i did, is a= 25/b

then instead of a i wrote 25/b

as

log 25/b - log b = 3

and then, should i use the division rule over here? or subtract rule?
Oh wow, I am kinda surprised myself.

Eh if you do it that way you get I believe log 25/b/b=log 64 tbh not too sure where you would go from there as I think the b's would cancel out and make log25=log64, maybe you can do it that way but it would be much easier in my opinion to do what I did, hopefully someone can explain this but I dunno

Edit: nevermind someone explained it above
12. (Original post by Olon)
https://c4a3f001dcd45afe69d0ceec8300...%20Edexcel.pdfFor Q6) whenever they ask you if it's a diameter do you use that formula?And can you help me with: 6c, q8b and 9a

Also, for question 4c if it was an underestimate how would i have explained the reasoning?
If you draw the trapezium (I guess it's a trapezium question lol :P) then the top of the trapezium will be below the graph line itself.

CIRCLE THEOREMS
Attached Images

14. (Original post by Elliemay97)
Hi I'm not sure how you can tell whether the estimate for the trapezium rule is an underestimate or an overestimate?
If the curve is like a U shape then its an overestimate, if its a N shape then its an underestimate
15. (Original post by Oz_Vessalius)
Yeah you can. It's probably best if you understand why it works based on the graphs but you don't strictly need to.
So for inverse sine answers, you do 180deg/pi minus theta to get your second solution and then add 2pi to each of those to get the rest
And for inverse cosine answers, you do 360deg/2pi minus theta to get your second solution and then add 2pi to each of those to get the rest.
Then for inverse tan solutions you just keep adding 180deg/pi.

CAST diagram has always confuse me too. If you are unsure your answers are correct always just plug them back into sin cos or tan functions and double check.

Yeah, you can always just draw the trapeziums that you are working out the area of and see for yourself whether you've got yourself an overestimate or an underestimate
That was really helpful, thanks. 2pi or if it's degrees i add 360 right?
16. (Original post by Haych97)

CIRCLE THEOREMS
Draw a triangle above the shaded bit and below it might help. That question is a real b**** unless you read the actual text properly, which after doing 50 line mechanics questions you don't!
17. (Original post by Haych97)

CIRCLE THEOREMS
What paper is this from?
18. If anyone could help me with the questions i asked before
19. https://c4a3f001dcd45afe69d0ceec8300...%20Edexcel.pdf

question 8c help
20. (Original post by NickLCFC)
What paper is this from?
Solomon Paper L

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