Question

(1)+(2+3+4)+(5+6+7+8+9)+.........the sum of n terms​

Answer 1

$n(n + 1) \div 2$

it is formula for n terms...

Answer 2

$HERE IS YOUR ANSWER$

formula is :-

n ( n + 1 ) ÷ 2

$\red{I HOPE IT'S HELP YOU}$