# C1 C2 - How did it go?Watch

12 years ago
#21
(Original post by Berto90)
One of the x co-ordinates was 10/3, what was the x co-ordinate of B.
I got 2 for A as 10/3 is bigger than 2, so was B
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12 years ago
#22
thnks!!
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12 years ago
#23
(Original post by purevengence)
sorry, i don't actually get that. how do you derive a sum-of-terms formula from a sum-to-infinity equation? i thought it just involved what Berto90 just said..
Ummm i wan't sure bout my answer but i think that it is correct...i dunno

well,,,

Sn = a(1-r^n)
.......--------- right?
...........1-r

and it said in the question that...
sum to infinity which is......a .....= 25
...............................--------
................................ ...1-r

therefore .....a .....x.....(1-r^n) = 25*(a-r^n)
..............------
.................1-r
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#24
(Original post by Berto90)
One of the x co-ordinates was 10/3, what was the x co-ordinate of B.
Lol, i meant to say "which was the x co-ordinate of B" .

I think I might've just got full marks
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12 years ago
#25
I couldnt do any of the sequences question. What did you all get for r and the proof? and I got n = 14. Did anyone else get this?
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12 years ago
#26
for the 25r^2 - 25r +4, i did the following

25 = a/(1-r), 25(1-r) = a
4 = ar, 4/r = a

make em equal

25(1-r) = 4/r

multiply out, 25 - 25r = 4/r
multiply both sides by r, 25r - 25r^2 = 4, rearrange, 25r^2 - 25r + 4 = 0

using the quadratic equation, you find r to be either 4/5 or 1/5.

using the greater of the two (as the question specifies) gives 4 = a(4/5), a = 5.

Did it ask for the smallest value to exceed 24? i cant remember

S_n < 24
a(1-r^n)/(1-r) < 24
5(1-(4/5)^n)/(1-4/5) < 24
.... (4/5)^n > 1/25
.... n*log(4/5) > log(1/25)
.... n > log(1/25) / log(4/5)
.... n > 14.4
n = 15 rounded up
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12 years ago
#27
(Original post by cat123)
I couldnt do any of the sequences question. What did you all get for r and the proof? and I got n = 14. Did anyone else get this?
wasnt n = 14.4.... and therefore u needed 15 as smallest value of n??
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12 years ago
#28
oh...i got n to be 14.235...so i rounded it down...
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12 years ago
#29
did everyone get 2 solutions for that tan trig question???
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12 years ago
#30
(Original post by cat123)
oh...i got n to be 14.235...so i rounded it down...
oh yeh it was something over 14... but even still i think u had to have integers? i think most of the questions iv seen like that want integers... dno could be wrong...

For the tan one, i got 78 deg and 360-78... something like that
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12 years ago
#31
I got 14.4 or something similar too, and I rounded it up to 15.

For the tan x = 5 question I got 78 deg and 180+78 deg
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#32
(Original post by cat123)
I couldnt do any of the sequences question. What did you all get for r and the proof? and I got n = 14. Did anyone else get this?
I ended up with n > 14.something

Therefore n=15. You'll definately get partial credit for n= 14 though I ould think.
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12 years ago
#33
im not sure about the tan question, but i think you have:

tan^-1(5) which equals 78.7 and then (180-78.7) = 101.3. Is that what everyone else got? Thats the only one i couldnt properly answer
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12 years ago
#34
i got that 14.235, and in below it wrote

"(n= 15 (whole number))"

is that all ok?
0
#35
(Original post by w00tt)

For the tan one, i got 78 deg and 360-78... something like that
I got 78.9 and 180 + 78.9, sionce tan is +ve in the third quadrant
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12 years ago
#36
I added 180 to the 78.7 but wasn't sure. It was worth 3 marks tho, where did the extra mark go?
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12 years ago
#37
(Original post by Berto90)
I got 78.9 and 180 + 78.9, sionce tan is +ve in the third quadrant
oh balls yeh... oh well, should only lose 1 mark
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12 years ago
#38
(Original post by mike_J)
im not sure about the tan question, but i think you have:

tan^-1(5) which equals 78.7 and then (180-78.7) = 101.3. Is that what everyone else got? Thats the only one i couldnt properly answer
it should have been 78.7 + 180...giving 258.7
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12 years ago
#39
Bah, what a bugger. Oh well. i think it was only a 2 mark question.
0
12 years ago
#40
did everyone get 10 for the radius of the circle when finding the equation for it???
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