Question

(Based on sum of n terms of A) (Arithmetic progression)Find the sum :

(i) 6 + 13 + 20 + ....to 19 terms.

(ii) (–3) + (–7) + (–11) + ...to 31 terms.​

Answer 1

Answer:

i)1311

ii)1953

Step-by-step explanation:

i)a=6,n=19 ,d=7 :. an = a +(n-1) d => 132

S = n/2 x (an+a)

=> 19/2X132+6

=) 138x19/2

=> 69x19

=) 1311

ii) a=-3, n=31, d = -4,:. an = a +(n-1)d=)-123

S= n/2 X (an+a)

=) 31/2 x-123-3

=) 63x31

=> 1953