Need some formula to do the competition well tomorrow?

Hello, I'm Diem from Vietnam, i'm 14 and i need your help.
I'll have a Doing-Math-By-Using-Casio-Caculator competition tomorrow and i'm afraid now because i don't have a well-preparation.
So i very need you. I want you to give me some formulas to do that quickly and exactly.

That's something about Trigonometry, arithmetic, algebra or everything you know

Thank you very much

Karnage2013-01-15T14:35:40Z

Favorite Answer

I realize that your competition has passed already, but a good arithmetic formula for the sum of natural numbers from 0 to n is n(n+1)/2