Question

if the 6 th term of an ap in -10 and its 10 th term is -26 ,then find its 20 th term​

Answer 1

4 (a+3d) = 5(a+4d)

4a+12d = 5a+20 d

a = -8 d

an = a+(n-1)d

For this to be zero , (n-1)d = -a

(n-1) d = - (-8d) ((which we derived previously)

(n-1) d = 8d

n- 1 = 8

n = 9

Therefore, 9th term is zero