Is it a Identity ?

[lvl107]

Hello,

I have a question, wish learning, and need help :

Thanks in advance for time and help.

Best regards,

Loi Le.

[lvl107]

and small extension with the above :

Thanks again.

Best regards,

Loi Le.

[RichardJ]

A sum from n=1 to n makes no sense. Do you mean a sum from n=1 to N (and on the RHS also replace n with N)?

[lvl107]

Many thanks for your help, Richard. Yes, I mean :

Regards,

Loi Le.

[lvl107]

And by modern convention then :

Regards,

Loi Le.

[lvl107]

and a bit of editing for the above :

Regards.