Question

If the 3rd and the 9th terms of an A.P. are 4 and − 8 respectively, then which term of this A.P is zero.​

Answer 1

Step-by-step explanation:

an=a+(n−1)d

a3=4

=a+2d ....(1)

a9 =−8

=a+8d ....(2)

∴4−2d=−8d−8

−2d+8d=−8−4

6d=−12

d=−2

a=4−2d

=4+4=8

a

n

=0,a=8,d=−2

0=8+(n−1)×(−2)

0=8−2n+2

2n=10

n=5