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Additional Math Help HERE ONLY...!

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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 :D

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 >.>

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