# Mathematics: Post your doubts here!

1357913579 thanx alot....=)

Silent Hunter said:
hey people i need help in permutations and combinations............any effective way of learning the techniques? any notes available ?
Same here....

Solve thz Identity:

( 1/sinx - 1/tanx )^2 = 1-cosx/1+cosx

#### 1357913579

are you giving statistics in this november

me?

#### Silent Hunter

well if ur asking from me............i am not giving the paper of stats ... AS maths + stats in 2012 june........

NEED HELP IN PERMUTATIONS AND COMBINATIONS!!!!

#### XPFMember

XPRS Moderator
Assalamoalaikum!!

For permutations and combinations watch this whole series of the tutorial, and you're good to go! http://www.examsolutions.co.uk/maths-re ... rial-1.php

I see people finding permutations and combinations hard, but honestly i enjoy it a lot..

And one more thing, (you may understand this better may be after you've gone through the topic, but anyways)
to make out when you have to use permutation (nPr of the calculator) and when to use combinations (nCr) , checck if the different arrangements of the selections will make any difference or not...if it does then you've to use nPr, and if it doesn't then u must use nCr.

Eg. lets say I want to choose two numbers from a total of three..how many possible selections are there?

now see i may choose 1 2 ; 1 3 ; 2 3
now the no. i've chosen can be written as 2 1 ; 3 1 ; 3 2

and obviously, this is giving me different numbers, so here arrangement does matter..so go for nPr => 3P2 = 6

but say if i got to chose 2 people from a total of 3 (A, B and C)

so possibilities are A B ; A C ; B/ C
and if i make this as B A ; C A ; C B
it doesn't make any difference as in the end there are the same people whether A first or B first....so that means arrangement does not matter...we'll use nCr => 3C2 = 3

P.S. These were pretty simple examples, I used them to explain the concept...you'll find this part of my explanation helpful when later on you tackle some more harder situations...this part really makes this thing easy...it did for me

#### nikhil000

nikhil000 said:
nikhil000 said:
nikhil000 said:
maths paper 3 oct nov 2010 P31 question no 2 . Plz i need help ...
thank you
,,Plz i need an urgent help!
..Plz help me out somebody
Anyone out there ..Plz help me!

#### XPFMember

XPRS Moderator
nikhil000 said:
nikhil000 said:
nikhil000 said:
maths paper 3 oct nov 2010 P31 question no 2 . Plz i need help ...
thank you
,,Plz i need an urgent help!
..Plz help me out somebody

Assalamoalaikum..

Check this:

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which question?

#### NehaKush

i nid notes on vectors paper3.. thnx

#### mrpaudel

ching293 said:
mrpaudel said:
ching293 said:

the first inequality is the inequality for the " perpendicular bisector of line joining (0,0) and (2,0)......whereas the 2nd inequality is for the " straight line starting from u making angle of pi/4 with the horizontal....!! now shade the common part..!!

the angle at point u looks like a or b?

I hope this will help...!! but a bit messy...sorry for that..!!

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#### mrpaudel

m lazy one..so wrote it in degree...u have to write it in radian from the very first...!! i think u know it....anyways..!! i hope it helped..!!

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