Mathematics: Post your doubts here!

[MustafaMotani]

Rutzaba i think u were lookin in wrong ms.. xD

 

[salvatore]

I put wrong inequalities there!! I am so sorry :/
For the first, it's 1 ≤ f(x) ≤ 3


Period does affect the range!!
E.g
sin(x) will have a range -1 ≤ f(x) ≤ 1 in the domain 0 to 2π
sin(½x) will have a range 0 ≤ f(x) ≤ 1 in the same domain!!

Oh yeah.. I think I got it.
Sin(1/2x) is half a cycle so it does not reach the negative axis! Don't tell me I'm wrong now

 

[Rutzaba]

Rutzaba i think u were lookin in wrong ms.. xD

lol sorry for wasting ur tym ^_^

 

[MustafaMotani]

lol sorry for wasting ur tym ^_^

anytime..

 

[daredevil]

7 (a) S
n = n² + 8n.
S
1 = 9 → a = 9
S2 = 20 → a + d = 11 → d = 2
(or equating n² + 8n with S
n and comparing
coefficients)
B1
M1 A1
[3]
co
Realises that S
2 is a + (a + d). co
(b) ara =− 9
30 2
arar =+
Eliminates a → 010133
2
rr =−+
or → 081572
2
aa =+−
→ r = ⅔
→ a = 27

Marking scheme Rutzaba

wth!! :O
and how did they come up with S1=9 ???? Gosh i'm gonna kill those freakking examiners!!! :O

 

[Dug]

Oh yeah.. I think I got it.
Sin(1/2x) is half a cycle so it does not reach the negative axis! Don't tell me I'm wrong now

Exactly!! For trig functions, you have to think like that.. It doesn't go lower towards the -1. If you keep the shape, domain and period in mind, you will never be wrong. A simple sketch can also prove very helpful!

 

[syed1995]

no dude part a
the ms is definitely wrong or may be the way theyy have done it is wrong

You're freaking out

Yea that's the answers i got.. I just shifted the 2 of n/2 to the other side to make it easier to work with

i got

d=2
16=2a-d
16=2a-2
2a=18
a=9

Answer

 

[syed1995]

Damn.. so many replies within minutes! No fair.. taking screenshots takes time

 

[syed1995]

wth!! :O
and how did they come up with S1=9 ???? Gosh i'm gonna kill those freakking examiners!!! :O

They plugged in n=1 in the n^2 + 8n equation.

 

[MustafaMotani]

daredevil
S1 = 9
when n=1 xD

 

[syed1995]

Maths is quite easy.. but our brains make simple questions so difficult :\

 

[daredevil]

You're freaking out

Yea that's the answers i got.. I just shifted the 2 of n/2 to the other side to make it easier to work with

i got

d=2
16=2a-d
16=2a-2
2a=18
a=9

Answer

i still don't get it... how did u get S1=9 ?? :'( sorry for the big time bother but this question is beating the hell out of me -___-

 

[daredevil]

Maths is quite easy.. but our brains make simple questions so difficult :\

ikr!! :O its like our megaminds are reall evil megaminds!! :O

 

[MustafaMotani]

daredevil just insert n= 1 in that Sn equation

 

[iKhaled]

i still don't get it... how did u get S1=9 ?? :'( sorry for the big time bother but this question is beating the hell out of me -___-

ok i only remember the first part of this question because this is a tricky question so i can't get it out of my mind till this day see

u have the total sum of all the terms formula given..if u substitute 1 in that formula it means u r finding the total sum of 1 term which is 9 so thats our first term got me ?

 

[daredevil]

Ok wow that was really a slap-in-face kind of simple!! :O x_x
thankuu so much iKhaled and MustafaMotani
i seriously don't know how these cie people do this!! they just get into ur heads and play mind games with u given just over an hour with them and them not even being present!! :O >__< urgghh

 

[iKhaled]

Ok wow that was really a slap-in-face kind of simple!! :O x_x
thankuu so much iKhaled and MustafaMotani
i seriously don't know how these cie people do this!! they just get into ur heads and play mind games with u given just over an hour with them and them not even being present!! :O >__< urgghh

CIE examiners r really experts because they know how even if u solved allll the past papers in the world for a subject, the one which u will do in the exam will be different to all of what u did and will be able to trick u!

 

[MustafaMotani]

daredevil .. lemme give yu a hint..
whenevr u get a tough question whch u think is out of syllabus... be sure that that question is the simplest one of all the questions in the paper

 

[syed1995]

MustafaMotani

"co (condone 27 or 1.5)"

http://papers.xtremepapers.com/CIE/...S Level/Mathematics (9709)/9709_s12_ms_12.pdf

In 7 part b.. does that mean if one wrote 27 and 1.5 he'd get the mark .. or just 27 is the possible answer?

Since the way I solved it in the end I got both of them as the answer.

 

[syed1995]

i still don't get it... how did u get S1=9 ?? :'( sorry for the big time bother but this question is beating the hell out of me -___-

Sn = n^2 + 8n
S(1) = (1)^2 + 8(1)
S1= 9

That way