Additional Math Help HERE ONLY...!

[shan2391]

Guys Q.4 on this past paper please i cant get the answer.

[vanibharutham]

Hey shan2391

The question is dealing with vectors and states this:

The points P, Q and R are such that QR = 4PQ. Given that the position vectors of P and Q relative to an
origin O are (6i + 7j) and (9i + 20j) respectively, find the unit vector parallel to OR.

Really simple question.
Let me break it down for you,

first they are asking you to find, the unit vector parallel to OR....

ok, so lets find the position vector of OR first,
To make the question easier,

lets just call it ( xi + yj )

The question also states that QR = 4PQ

What is QR ?

( xi + yj ) - ( 9i + 20j )
This statement can join to give single component vectors:

QR => (x - 9)i + (y - 20)j

Next, what is 4PQ?

4[ ( 9i + 20j ) - (6i + 7j) ]
=> 4[3i + 13j]
12i + 52j

ok,
now equate the equation:

(x - 9)i + (y - 20)j = 12i + 52j

and solve for the i's and j's separetely

therefore,

x - 9 = 21
x = 21

and

y - 20 = 52
y = 72

Giving us a position vector for R ( 21 i + 72 j)

Finding the unit vector is the easy bit

1/Magnitude of the vector * (21 i + 72 j )

=> (21 i + 72 j) / 75

[shan2391]

Thanks a lot  vanibharutham

[Padapop]

Paper 1 tmmr :O

[sweetsh]

=(

[someone]

could any1 help me how to solve equations like this:

nC2=45

shuld we just try any combination using the calculator, or is there any other way to solve this?  

thx

[vanibharutham]

nC2 = 45

and we have to find n

Really simple again

we know that nC2 = >

n(n-1)
2

and that equals to 45

so therefore,

n(n-1) = 90
n²-n-90 = 0
(n+9)(n-10)=0
n = -9 and n = 10
we cant any have any negative numbers in combinations, therefore n = 10 only

and then u can check this using your calculator:


10C2 = 45

You must remember the formula for combinations, though i think it is in the front page...

nCr =

n!
(n-r)!r!

therefore, when we have nC2 =>

n(n-1)(n-2)......etc
(n-2)(n-3)...etc * 2!

which simplyly leaves us with

n(n-1)
2

hope that helped

[Padapop]

Are there any ways of knowing which direction is the wind coming from eg in relative velocity?

Eg Due west - GOING TOWARDS WEST ?

From north west eg from 135 degree angle or something?

[vanibharutham]

i highly dislike those questions....

But you have to break it down into simple and usable steps...and make sure u can work out all the angles

If it says,

The wind is blowing from the south-east, you know it will be blowing on a bearing of 045, because south-east is exactly that.

If it blows due north, then it is perpendicular

[divineobsidian]

is anyone good on those relative velocity questions with the river. usually when its aircraft bearings are always used from north right? but whenever i meet a river question i never really know which angle the question means >.>

[igexam]

does anyone have additional math question papers and markschemes from 1993 to 2000??

If so, I would be very glad if you could send them to divakarbala@gmail.com

[vanibharutham]

is anyone good on those relative velocity questions with the river. usually when its aircraft bearings are always used from north right? but whenever i meet a river question i never really know which angle the question means >.>

Divine obsidian,

Its not only aircraft bearings that are taken from the north. Any BEARING will always be taken from the north.

For the river questions,
if you are unsure, i suggest you find all possible angles, there seems no way i can explain through this forum...

[EVIL DOCTOR]

can someone help me with ln,log,e fuctions

[Padapop]

Paper 2 May june 2004

Question 4

(1 + sec x) (cosec x - cot x) = tan x

Prove the identity. Shoot thats hard.

[Padapop]

Oh nvm i got it