Question

-6-2+2+6+.......up to 21 th term .find the sum​

Answer 1

Given :-

a = -6

d = 4

n = 21

TO FIND :- Sum of 21 terms i.e. S.21

SOLUTION:-

Sn = n/2 * [2a + (n-1)d]

Sn = 21/2 [ 2 x -6 + 20 x 4]

Sn = 21/2 [ -12 + 80]

Sn = 21/2 [-12+80]

Sn = 21/2 x 68

Sn = 21 x 34

Sn = 714 (ANS)