Question

Which term of the AP : 21,18,15,........is -81? Also, is any term 0?

Answer 1

-81:
-81=21+(n-1)(-3)
-81-21=(n-1)(-3)
-102/-3=(n-1)
minus minus get cancelled.
so,
n-1=102/3
n-1=34
n=35
so, 35th term is -81

Answer 2

Answer:

35

Step-by-step explanation:

a1 = 21                                                            d = a2 - a1

a2 = 18                                                              = 18-21 = -3

an = -81 = a1 + (n-1) d

  -81 = 21 + (n-1) (-3)

 -81  = 21 - 3n + 3

 -81 = 24 - 3n

 -81 - 24 = -3n

-105

-------    = n

-3

n = 35