Question

Va rog ajutati-ma!

Calculati:
3+6+9+12+...+2001

Answer 1

Simplu 3+6+9+12...+1999+2001=444889

Answer 2

$\displaystyle 3+6+9+12+...+2001=3(1+2+3+...+667)= \\ \\ =3 \times \frac{667(667+1)}{2} =3 \times \frac{667 \times 668}{2} =3 \times \frac{445556}{2} = \\ \\ =3 \times 222778=668334$