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# Edexcel Maths C3 watch

1. havent revised
not gonna revise
oh well
2. crap crap crap can't do any of it
3. (Original post by jlcf)
First re-arrange equation to in terms of y:

y = [ arcsin(x/4) - 6 ] / 2

Then sub y into the dy/dx:

dy/dx= 1 / 8cos(2y+6) =>

= 1 / 8cos{2[arcsin(x/4)-6]/2 +6} times 2 and divide 2 => 1 / cancels out
-6 and +6 => 0

= 1 / 8cos[arcsin(x/4)]

Now arcsin(x/4) is the same as sin feta = x/4 ... draw triangle with opposite as 4 and hypotenuse as x

Find adjacent which is √4² - x² => √16 - x²

Cos feta is √16 - x² / 4 (ajacent over hypothenuse)

= 1 / 8cos[arcsin(x/4)] = 1 / 8 (√16 - x² / 4 )

=> 1 / 2 √16 - x²

Sorry hard to explain! Hope it helps!
Ah ok cheers..at least I understand it a bit better!

Hoping for nothing like this tomorrow :O
4. help with these questions needed.

https://eiewebvip.edexcel.org.uk/Rep...e_20070118.pdf

2b and c thanks.
5. (Original post by houseo2)
help with these questions needed.

https://eiewebvip.edexcel.org.uk/Rep...e_20070118.pdf

2b and c thanks.
2b complete the square
2c numerator>0, look at denominator
6. (Original post by houseo2)
help with these questions needed.

https://eiewebvip.edexcel.org.uk/Rep...e_20070118.pdf

2b and c thanks.
For 2b you can also differentiate and find the minimum point of the curve. It will have a y value more than zero, proving that f(x) is always >0
7. who else is sitting the exam tomorrow? i did it in january and i got 83 but im resitting to try and boost my chance of an a*
i have done all the past papers and im feeling alot more confident about it than in january!
8. Feeling ready for this exam - should get over 90UMS.
9. I am sitting it =] You did really well! I am sitting it for the first time and I don't have high expectations ahaha!
10. (Original post by Mr ABC)
2b complete the square
2c numerator>0, look at denominator
i know howto complete square but am unsure for this question could show how to do it
11. (Original post by game well and truly over)
The sine of 2y+6 is x over 4. Doesnt matter what you call the angle, in this case, 2y plus 6. Call it theta or whatever. Draw a triangle whose opposite side is length x, with hypotenuse 4. Then the length of the adjacent side is the sq root of (16 minus x squared). The cosine is therefore root(16-x squared) over 4. The dreivative is therefore the inverse. See now? Much easier than all those complex explanations involving arcsin etc.
i understand up until the inverse bit you said.
12. trigonometry
how should we go about these questions? in the exam i usually panic and cant think properly
13. (Original post by houseo2)
i know howto complete square but am unsure for this question could show how to do it
if i remember right, it was x^2 + x + 1

complete the square, =(x+0.5)^2 +0.75

any real number squared >=0, so clearly the above >= 0.75
14. I'm just wondering in our working at differnt stages, if we don't have an exact value how many sig fig should we work with to avoid accuracy errors?

Thanks
15. After solving too many questions on trigonometry I found out it's very easy and most questions on this topic are the same.
16. (Original post by FZka)
After solving too many questions on trigonometry I found out it's very easy and most questions on this topic are the same.
same in what sense?
As in the "prove" questions and "solve"?
I dont see double angles appearing a lot in the papers, what do you think? Also, I havent learnt the sum and product rules, do you think its important to know them?
17. 3 sf
18. Just want to get this exam out the way now! I must remember to revise inverse trig graphs and graphs of cot/sec/cosec !
19. how do you do this question

cosec^2 2x - cot2x = 1

solve for 0 - 180 degrees

7 marks
20. (Original post by dunnoaboutme)
how do you do this question

cosec^2 2x - cot2x = 1

solve for 0 - 180 degrees

7 marks
What paper? Who questions are easier for these.

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