Question

Please explain step by step(Question of Arithmetic Progressions)
(1)+(1+1)+(1+1+1)+...+(1+1+1+...n-1 times) =? ​

Answer 1

Step-by-step explanation:

First term, a= 1

last term, l = n-1

no of terms = n-1

Sum= (n-1)/2 × { 1 + n-1}

as in S= (no.of terms)/2 × { a + l}

= (n-1)/2 × (n)

= n(n-1)/ 2