Question

3+6+9+12+.....+2001=
CALCULATI

Answer 1

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

Answer 2

Teorema lui Gauss
3(1 + 2 + 3 + ... + 667) = 667 * 668 : 2 = 667 * 334 = 222.778 * 3 = 668.334