Author Topic: Hellllllllllllllllllllllllllllllllllllllllllp , Arithmetic Progression !!  (Read 4434 times)

Offline ~HyDrOgEn~

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Show that 28,23,18,13 ... , is arithmetic , .Hence find Un and the sum of the first n terms in the simplest form ??

Offline ~HyDrOgEn~

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Hey golden girl  , it was really nice to meet you after  The IGCSE has finished , i appreciate that you are helping , but i didn't get it , can you please re Explain
thanks :D

Offline The Golden Girl =D

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Nice to see you around too =D

I sent my friend a sg hopefully you'll find the answer later or perhaps by tomorrow =]
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Freaked12

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Show that 28,23,18,13 ... , is arithmetic , .Hence find Un and the sum of the first n terms in the simplest form ??

a+(n-1)d
 28+(n-1)-5
31-5n

second part

sum of first n numbers
n/2(2a+(n-1)d)
 n/2(2*28+(n-1)-5)
(-5n^2+61n)/ 2
« Last Edit: December 20, 2010, 05:16:18 pm by Requiem~Katie »

Offline Deadly_king

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Show that 28,23,18,13 ... , is arithmetic , .Hence find Un and the sum of the first n terms in the simplest form ??

For the sequence to be an arithmetic progression it should fit in the equation Un = a + (n-1)d where a : First term, d : common difference and n : term number.

The sequence is arithmetic since the common difference is constant, i.e U1 - U2 = U3 - U4

So from the sequence we can not that the common difference is -5 -----> U2 - U1 = 23 - 28 = -5 or U4 - U3 = 13 - 18 = -5.

So now we just need to replace a = 28 and d = -5 in the formula ----> Un = 28 + (n - 1)(-5) ----> Un = 33 - 5n

Requiem made a little mistake there. ;)

Equation for the sum of n terms in an A.P = 0.5n(2a + (n - 1)d)

Again you just need to replace a = 28 and d = -5 ----> Sn = 0.5n(2(28) + (n-1)(-5))

Just simplify to get Sn = 0.5n(61 - 5n) or Sn = (61n - 5n2)/2


Freaked12

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It was only 33 instead of 31 :O.You wrote the whole answer

Offline Deadly_king

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It was only 33 instead of 31 :O.You wrote the whole answer

Sorry dude.

Indeed you did it well but I just wanted to help Hydrogen to understand and not just copy the answer.

Hope you don't mind. :-[

Freaked12

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Oh okay
No problem

:)

Offline Deadly_king

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Oh okay
No problem

:)

Thanks for your comprehension. :D

Offline Arthur Bon Zavi

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Thanks for your comprehension. :D

Which chapter is this from, from CIE Mathematics books (Pure mathematics, Mechanics or Statistics)?

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Offline ~HyDrOgEn~

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Re: Hellllllllllllllllllllllllllllllllllllllllllp , Arithmetic Progression !!
« Reply #10 on: December 21, 2010, 01:30:19 pm »
Which chapter is this from, from CIE Mathematics books (Pure mathematics, Mechanics or Statistics)?

It's not cie mathematics , Its IB :)

Offline Arthur Bon Zavi

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Re: Hellllllllllllllllllllllllllllllllllllllllllp , Arithmetic Progression !!
« Reply #11 on: December 21, 2010, 01:53:39 pm »
It's not cie mathematics , Its IB :)

I asked the chapter. ;D

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Offline Deadly_king

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Re: Hellllllllllllllllllllllllllllllllllllllllllp , Arithmetic Progression !!
« Reply #12 on: December 21, 2010, 02:25:52 pm »
Which chapter is this from, from CIE Mathematics books (Pure mathematics, Mechanics or Statistics)?


Pure Maths 1

Chapter 8 ----> Sequences

@ Hydrogen : It may be IB but it's also found in CIE. ;)

Offline Arthur Bon Zavi

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Re: Hellllllllllllllllllllllllllllllllllllllllllp , Arithmetic Progression !!
« Reply #13 on: December 21, 2010, 02:28:46 pm »
Pure Maths 1

Chapter 8 ----> Sequences

@ Hydrogen : It may be IB but it's also found in CIE. ;)

I see. 8)

Unfortunately we are not yet done with this chapter.
We are going to start this chapter soon, after completing whole S1. :D

S1 is my left hand game now ! ::)

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- NU

Offline Deadly_king

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Re: Hellllllllllllllllllllllllllllllllllllllllllp , Arithmetic Progression !!
« Reply #14 on: December 21, 2010, 02:33:26 pm »
I see. 8)

Unfortunately we are not yet done with this chapter.
We are going to start this chapter soon, after completing whole S1. :D

S1 is my left hand game now ! ::)

Ooh......................I had completed the whole p1 and p3 before moving to S1 and M1. ;D

Nice.......keep up the good work. :)