Question

Calculati : -2-4-6-...-2000

Answer 1

$S=-2(1+2+3+...+1000)= \\ \\ ~~~=-2 \cdot \frac{1000 \cdot 1001}{2}= \\ \\ ~~~=-1000 \cdot 1001= \\ \\ ~~~=\boxed{-1001000}$

Answer 2

S=-2(1+2+3+...+1000) = (-2x1000x1001)/2 = -1001x1000 = -1001000