Math Is Fun Forum

soha

Real Member

Registered: 2006-07-07

Posts: 2,530

Summation

Find the sum of 20 terms of the series

Solution:-

Let us find

and then

...................

how did they get that

?I have made that part bold.

another question, in the next step , how do we get that bold and underlined  part there???

Please answer as fast as you can . Thank you.

Last edited by soha (2010-05-20 17:24:55)

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"Let us realize that: the privilege to work is a gift, the power to work is a blessing, the love of work is success!"
- David O. McKay

soha

Real Member

Registered: 2006-07-07

Posts: 2,530

Re: Summation

why does underline, bold function not work here??

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"Let us realize that: the privilege to work is a gift, the power to work is a blessing, the love of work is success!"
- David O. McKay

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Summation

The Tn is the general term form the terms you trying to sum.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

soha

Real Member

Registered: 2006-07-07

Posts: 2,530

Re: Summation

i know it . But how did they get it as n.2n=1wholesquare???

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"Let us realize that: the privilege to work is a gift, the power to work is a blessing, the love of work is success!"
- David O. McKay

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Summation

Usually it is given to you in the problem or you will have to guess it yourself. Or generate it by using any curve fitting idea.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

soha

Real Member

Registered: 2006-07-07

Posts: 2,530

Re: Summation

it is not given in the problem. How to generate myself?
curve fitting idea???

Last edited by soha (2010-05-20 15:10:09)

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"Let us realize that: the privilege to work is a gift, the power to work is a blessing, the love of work is success!"
- David O. McKay

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Summation

That isn't easy to do. Usually it is guessed at and then proven by induction. Even for curve fitting you will have to guess at the form you want to fit. You can use differences but that requires a little bit more knowledge. Also to fit you will have understand a little bit about simultaneous equations and solving them.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

soha

Real Member

Registered: 2006-07-07

Posts: 2,530

Re: Summation

what about my other question?

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"Let us realize that: the privilege to work is a gift, the power to work is a blessing, the love of work is success!"
- David O. McKay

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Summation

I can't see the bold part.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

soha

Real Member

Registered: 2006-07-07

Posts: 2,530

Re: Summation

some thing enclosed in  tag

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"Let us realize that: the privilege to work is a gift, the power to work is a blessing, the love of work is success!"
- David O. McKay

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Summation

Sorry I don't know what S2O is. You latex has not come through.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

soha

Real Member

Registered: 2006-07-07

Posts: 2,530

Re: Summation

what must I do to it?

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"Let us realize that: the privilege to work is a gift, the power to work is a blessing, the love of work is success!"
- David O. McKay

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Summation

Try this first:

{\bf Hello} World!

The \bf is bold font.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

soha

Real Member

Registered: 2006-07-07

Posts: 2,530

Re: Summation

\bf for making it bold????

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"Let us realize that: the privilege to work is a gift, the power to work is a blessing, the love of work is success!"
- David O. McKay

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Summation

Yep, but you are going to have to experiment for math. It is primarily for text it seems

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

soha

Real Member

Registered: 2006-07-07

Posts: 2,530

Re: Summation

I think I did it. What about underline?

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"Let us realize that: the privilege to work is a gift, the power to work is a blessing, the love of work is success!"
- David O. McKay

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Summation

Work with this:

\underline{x+y}

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

soha

Real Member

Registered: 2006-07-07

Posts: 2,530

Re: Summation

I underlined it. Now please see the bold underlined part. Explain me how they got that there?

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"Let us realize that: the privilege to work is a gift, the power to work is a blessing, the love of work is success!"
- David O. McKay

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Summation

Hi soha;

What that underlined part is, is someone trying to get the answer and not succeeding.

The answer is:

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

soha

Real Member

Registered: 2006-07-07

Posts: 2,530

Re: Summation

It cannot be like that. It is given in the solved examples section of my textbook. They cannot be wrong

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"Let us realize that: the privilege to work is a gift, the power to work is a blessing, the love of work is success!"
- David O. McKay

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Summation

Hi soha;

Checked it 3 times the answer is above. Have you copied the problem right. Please check your latex again.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

soha

Real Member

Registered: 2006-07-07

Posts: 2,530

Re: Summation

I copied it correctly. I  will check it again

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"Let us realize that: the privilege to work is a gift, the power to work is a blessing, the love of work is success!"
- David O. McKay

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Summation

Hi soha; For the indefinite summation that is the answer above.

You made a mistake it is not

It is:

For the definite summation, the answer you have in post#1 is correct.

A little background:
Notice the difference between this sum and the one in post #18 . This one below is a definite sum. See the indices? k from 1 to n. The sum in post #18 does not have that. It is an indefinite sum.

Now you just plug in n = 20 into the RHS of the above expression.

To do this sum manually. You break the sum into pieces. Then you handle each piece by the rules of the summation calculus. Or you can use a set of tables, or a curve fitting idea.

That is the sum of the first 20 terms.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

ZHero

Real Member

Registered: 2008-06-08

Posts: 1,889

Re: Summation

Look at any term, say 3(7[sup]2[/sup]), and you'll observe that 7 = (2×3+1)

observe... T[sub]1[/sub] = 1(3)[sup]2[/sup] = 1(2×1+1)[sup]2[/sup]

T[sub]2[/sub] = 2(5)[sup]2[/sup] = 2(2×2+1)[sup]2[/sup] etc

We can say that T[sub]n[/sub]= n(2×n+1)[sup]2[/sup]

NOTE: Its true that you'll have to guess it.
Most of the times, they will always be easy (of the form n(an+b)) in the questions given in your textbooks and exams.
Curve fitting is another idea that you just don't need in your school.

Last edited by ZHero (2010-05-20 20:14:14)

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If two or more thoughts intersect, there has to be a point!

ZHero

Real Member

Registered: 2008-06-08

Posts: 1,889

Re: Summation

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If two or more thoughts intersect, there has to be a point!