Question

Which term of the AP : 21,18,15,........is -81? Also, is any term 0? reason for your answer .​

Answer 1

Answer:

a = 21

d = 18 - 21

= -3

l = -81

n term is = a+(n-1) d

21+ (n-1) -3 = -81

-3n +3 +21 = -81

- 3n = -81-24

n = -105/-3

35

a+(n-1) d = l

21 + (n-1) -3 = 0

21 -3n +3 = 0

-3n = -24

n = -24/-3

n = 8

Answer 2

Let "h" term of Ap be -81.

Then common difference =18-21=-3

now by question,

21+(h-1)(-3)=-81

or 21-3h+3=-81

or 3h=24+81

or h=105÷3

or h=35

Therefore the 35th term of AP is -81.

Again let us assume that "n"term of AP is 0.

Then

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

21-3n+3=0

or 3n=-24

or n=-8,which is not a natural number.

Therefore 0 is not included in the AP.

Hope this will help you.