Question

which term of the AP 21, 18, 15 ..., is zero____________​

Answer 1

Answer:

8th term is zero.

Step-by-step explanation:

0 = 21 + ( n - 1 ) (-3)

0 = 21 + ( -3n + 3 )

0 = 21 + 3 - 3n

0 = 24 - 3n

3n = 24

n = 24/3

n = 8

Answer 2

$\huge{\boxed{\boxed{\tt{\sf{\red{A{\green{n{\orange{s{\blue{w{\pink{e{\purple{r}}}}}}}}}}}}}}}}$

a = 21

d = 18 - 21 = -3

l = 0

l = a +(n - 1)d

0 = 21 +(n - 1)-3

-21 = (n - 1)-3

-21/-3 = (n - 1)

7 = n - 1

n = 7 + 1 = 8

∴ Eighth term of the AP 21, 18, 15 ..., is zero.