Product of two finite summations

Its so faint! I can't make out most of the notation

I was wondering what the product of two finite summations was and I stumbled upon this formula:

(I would have re-written it in LaTex but I can't seem to get the upper and lower bound above and beneath the sigma).

I don't really understand the formula so if someone could show me how it works with an example, it would be much appreciated.
Thank you in advance!

(I would have re-written it in LaTex but I can't seem to get the upper and lower bound above and beneath the sigma).

Yeah... that thing came up at uni... we have to 'Be aware of it' and be able to do it by hand up to 'n' terms for n<10 or so - there isn't really an easy way without a short program on a computer as far as I know

But surely you understand the formula? Because I literally don't understand the notation.

means (a1+a2+a3+...+an)(b1+b2+b3+...+bm) where n=/=m

Wouldnt it be equal to $(a_0+a_1+a_2+...+a_n)(b_0+b_1+b_2+...+b_n)$ ?
And what's $m$?

Wouldnt it be equal to $(a_0+a_1+a_2+...+a_n)(b_0+b_1+b_2+...+b_n)$ ?
And what's $m$?

I was wondering what the product of two finite summations was and I stumbled upon this formula:

(I would have re-written it in LaTex but I can't seem to get the upper and lower bound above and beneath the sigma).

I don't really understand the formula so if someone could show me how it works with an example, it would be much appreciated.
Thank you in advance!

Looking at the website I think it deals specifically with the upper limit being n for both series.

Where are you struggling exactly - have you used the sigma notation before, or is it all totally unfamiliar to you?

yup, but the series don't have to have the same number of terms - hence n and m numbers of terms