Question

... 16th term of an A.P in 78. 5. Find the number of terms in each of the following APs: 18,15 1/2,13​

Answer 1

Step-by-step explanation:

a=18

d=a

2

−a

1

=15

2

1

−18

⇒d=

2

31−36

=

2

−5

Considering there are n terms in this A.P.

a

n

=−47

We know, a

n

=a+(n−1)d

−47=18+(n−1)(−

2

5

)

⇒−47−18=(n−1)(−

2

5

)

⇒−65=(n−1)(−

2

5

)

⇒n−1=

−5

−130

=26

⇒n=27

The series has 27 terms.