The long question

You can use this formula to find the sum of 'n' terms of natural numbers. $\\ \\ \frac { n\quad *\quad (n+1) }{ 2 }$

n = 1000000000

Therefore,

$=\frac { 1000000000\quad *\quad (1000000001) }{ 2 } \\ =\frac { 500000000\quad *\quad (1000000001) }{ 1 } \\ =500000000500000000\\$

1+2+...100=5050, that's just 100/2 then put 2 50 in the front. 1+2+...1000=500500, it's the same thing, so 1+2+...1000000000=500000000500000000