Question

TUTORIAL on Arithmetic Progression (AP or Arithmetic Sequence), Geometric Progression (GP), Harmonic Progression(HP). This was one of my favorite topics in junior college.

P.S.: This is my first tutorial. So don’t be hard on me :P

Answer 1

\[\large{\color{Blue}{T}\color{Yellow}{U}\color{Magenta}{T}\color{Pink}{O}\color{MidnightBlue}{R} I\color{Blue}{A}\color{Green}{L}!}\]
\[\color{Red}{Arithmetic Progression (AP):}\]
A sequence is in arithmetic progression when its next term to previous term ‘difference’ is always constant. As an example, if I say a frog jumps every 2 seconds starting right now which we take as t=0 sec, the next jump will be on t=2 sec.
When will the next jump be?
Yes, you are correct, it will be at t=4 sec.
Now how did u get 4 ?
Let me tell you, you added the difference d=2 to previous term (2).
So to get next term of AP you always add the common difference to current term, and to get previous term you always subtract the common difference from current term.
A more general formula to get the ‘n’ th term of an AP is:
\[T_n=a_1+(n-1)d\]
Where a_1is the first term and d is the common difference of the AP.
So the general terms of AP are
\[ a_1, a_1+d,a_1+2d,a_1+3d,…..a_1+(n-1)d.\]
When needed to find the sum of ‘n’ terms of an AP, you use:
\[S_n=\frac{n}{2}(2a_1+(n-1)d)\]
But you have a shortcut formula, when you have the 1st and the last term of AP:
\[S_n=\frac{(a_1+a_n)}{2}\] ,where an is the last term.
The sum of infinite Arithmetic Sequence is essentially infinite. But, if a=b=0,the sum is 0.
The product of ‘n’ terms of a finite AP is
\[d^n \frac{\Gamma(a_1/d+n)}{\Gamma(a_1/d)}\]
when a1/d is positive integer.
Note: Ignore this if you are unfamiliar with Gamma Functions.
\[\color{Red}{Geometric Progression (GP):}\]
A sequence is in arithmetic progression when its next term to previous term ‘ratio’ is always constant.
Classical example of Geometric progression is population growth.
If I say population doubles every 15 years, what does it mean?
If the population is 7 billion in 2012, the population in 2027 will be 14 billion.
So what will be the population in 2042?
Yes! you are again correct it will be 28 billion.
How did u get 28?
You multiplied 14 by common ratio 2 to get 28.
So to get next term of GP you always multiply the common ratio to current term, and to get previous term you always divide the current term by common ratio.
A more general formula to get the ‘n’ th term of a GP is:
\[T_n=a_1r^{n-1}\]
Where a1 is the first term and r is the common ratio of the GP.
So the general terms of GP are
\[a_1,a_1r,a_1r^2,…..a_1r^{n-1}.\]
When needed to find the sum of ‘n’ terms of a GP, you use:
\[S_n=a_1\frac{(1-r^n)}{(1-r)}\] when |r|<1
\[S_n=a_1\frac{(r^n-1)}{(r-1)}\] when |r|>1
The sum of infinite geometric sequence with |r|>1 , is essentially infinite.
The sum of infinite geometric sequence with |r|<1 , is
\[S_ \infty=\frac{a}{(1-r)}\].
The product of ‘n’ terms of a finite GP is
\[P=(a_1a_{(n+1)})^{\frac{(n+1)}{2}}\]
\[\color{Red}{Harmonic Progression (HP):}\]
I would call HP as reciprocal of AP, because if we take the reciprocal of the terms in AP, the new terms would be in HP or equivalently, if we take the reciprocal of the terms in HP, the new terms would be in AP.
The general terms of HP are :
\[a_1,\frac{a_1}{(1+d)},\frac{a_1}{(1+2d)}….\frac{a_1}{(1+(n-1)d)} \]
There is no accurate simple general formula for sum to ‘n’ terms of the series.

______________________________________________________________________
Now, lets play with only 3 term sequences.
If a,b,c are in AP, then b is the arithmetic mean(AM) of a and c and is given by
\[b=\frac{(a+c)}{2}\]
This you get from the fact that the difference between consecutive terms are equal,so b-a=c-b or a+c=2b or b=(a+c)/2
If A,B,C are in GP, then B is the geometric mean(GM) of A and C and is given by
\[B=\sqrt{AC}\]
This you get from the fact that the ratio between consecutive terms are equal,so A/B=B/C,so AC=B^2
So B=sqrt(AC).
If X,Y,Z are in HP, then Y is the harmonic mean(HM) between X and Z given by
\[Y=\frac{2XZ}{(X+Z)}\]
Also, this relation is very useful :
The geometric mean of 2 numbers is the geometric mean of arithmetic mean and harmonic mean of those two numbers.
Meaning:
\[GM^2=AM.HM\]
Or here
\[B^2=b.Y\](if a=A=X,c=C=Z)

Answer 2

u have great skill in Progressions...:)

Answer 3

thanks :) as i told it was my favorite topic,so i practiced a lot...

Answer 4

Can...u Do AGP @hartnn

Answer 5

my initial intention was to include AGP also and typical examples of it,but this tutorial was already long enough!

Answer 6

you guys have patience

Answer 7

what's up with those kinds of latex lol

Answer 8

great work........

Answer 9

@Abhishekjha PLZ SEE THIS

Answer 10

Man! I have trouble with this site sometimes. I can't seem to message people and I can't read the LaTeX on this posting.

Answer 11

Maybe,because of slow net speed....

Answer 12

I have pretty good gear and connection speed, but I frequently seem to have compatability issues. I turned off pop up blocker, but still no messages out. I love this site, so I will keep investigating. If I get to the point where I can read it, I would be happy to thoroughly check this posting out. Thank you for pointing it out.

Answer 13

ok,thanks for your time :)

Answer 14

Nice turorial hartnn

Answer 15

Use \; , \: , \quad or \qquad to give spaces between two words..

Answer 16

Actually, AP is my favorite topic..

Great work @hartnn ..

This will help a lot..

Answer 17

thanks @waterineyes
i used {space} for spaces,though not here...

Answer 18

Great work @hartnn

Answer 19

And don't think I am trying to hard on you..

Ha ha ha...

Answer 20

even i don't think that :)
thanks for wonderful replies, @waterineyes and @ajprincess

Answer 21

Oh @hartnn sorry to say, but you are missing \(\color{blue}{n}\) in Sum formula for AP..

The Second sum formula that is related to fist and last terms..

Answer 22

*first..

Answer 23

oh yes!
thanks for pointing it out.
\[S_n=n\frac{(a_1+a_n)}{2} \]

Answer 24

i don't think i can edit that now.....can i?

Answer 25

Yes you can..

Answer 26

Copy the whole text and go to "Ask a Question" box and paste it their..


Ha ha ha ha...

Answer 27

Oh God my english..

*there..

Answer 28

yeah,i can always do that :P
but m gonna ask a new question.....

Answer 29

Yeah sure why not..

Answer 30

any suggestions for next tutorial?
i am thinking about:
1. Definite integration.
2.Partial Fractions.
3.Limits.
4.Solving 3rd degree Equation(1 variable)
Which ONE should i give next?
or any other topic whose questions asked by many...??

Answer 31

In my opinion, Go for Limits or Definite Integrals..

Limits being the first preference..

Answer 32

and also 4...including rational root theorem

Answer 33

ok,i'll first write on solving cubic eq as it will be short,then next week on limits as it will be long.

Answer 34

Sure..

Answer 35

Excellent , i must say you are Oracle in AP :)

Answer 36

thanks :)

Answer 37

this is good ..

Answer 38

thanks :)

Answer 39

thi is so helpful . i hope i will answer my quiz for monday on school .

Answer 40

wow, amazing. It seems helpful:)

Answer 41

thanks :)

Answer 42

thnx. it is so helpful... @hartnn

Answer 43

welcome ^_^

Answer 44

I like to post on dead threads.

Answer 45

^ same :P
But good job @hartnn !!