Use the formula S =(n + 1)2 to find the sum of 1 + 2 + 3 + ... + 780.
1 + 2 + 3 + ... + 780 =
[ 780 x 781] / 2 =304,590
Guests answer is correct but your formula is wrong
This is what it should be.
S=n(n+1) / 2
