sigma notation (1 Viewer)

[gouge.away]

...when summing an AP. the proper use of this eludes me.

any help would be much appreciated.

 

[jet]

I tried to explain it as easily as possible. I don't think I did that really. Sorry.

 

[lychnobity]

...when summing an AP. the proper use of this eludes me.

any help would be much appreciated.

Ok, in your example, the 20 at the top means they want the sum of 20 terms

The k=4 means you start with 4, and from there go on to sub 5,6,7.. all the way to 24 (they want 20 terms remember) into the formula 2k-5.

So, you apply the formula 2k-5 to numbers 4 to 24 (coz they want 20 terms), and add the results.

 

[jet]

Lol.... I didn't even notice that. I'm such an idiot.

 

[gouge.away]

thanks!

 

[gouge.away]

Lol.... I didn't even notice that. I'm such an idiot.

I think you were replying while I was fiddling with the LaTex thing. Sorry about that.

 

[xFusion]

Ok, in your example, the 20 at the top means they want the sum of 20 terms

The k=4 means you start with 4, and from there go on to sub 5,6,7.. all the way to 24 (they want 20 terms remember) into the formula 2k-5.

So, you apply the formula 2k-5 to numbers 4 to 24 (coz they want 20 terms), and add the results.

Doesn't the 20 at the top mean 20 is the last term?

 

[Uncle]

Doesn't the 20 at the top mean 20 is the last term?

Not if it doesn't start from 1.

e.,g.

[maths]\sum_{x=19}^{20} x = 19 + 20 = 39[/maths]


But when in uni mathematics, there is often an infinity symbol.
It doesn't mean you keep writing non-stop.

e.g.

[maths]\sum_{x=1}^{\infty} x = 1 + 2 + 3 + 4 ...[/maths]