Question

3(1+2+3+4+...+1000)+(3+4+5+...+1000)•(-3)=

Answer 1

3(1+2+3+4+...+1000)+(3+4+5+...+1000)•(-3)=
=3(1+2)+3(3+4+...+1000)-3(3+4+5+...+1000)=
=3•3=9

Answer 2

1+2+3+4+....+1000
n (n+1):2
1000 (1000+1):2
1000×1001:2=1001000:2=500500
3+4+5+...1000
1000 (1000+3):2
1000×1003:2=501500
(3×500500)+501500 (-3)=
1501500-1504500= 3006000