Question

if third term of ap is 18 and seventh term of 30 find the series​

Answer 1

Step-by-step explanation:

Let the first term of an AP be a and common difference be d

The third term of an AP is a+2d, given that it is equal to 18

⇒a+2d=18

The seventh term of an AP is a+6d, given that it is equal to 30

⇒a+6d=30

By subtracting first equation from second equation , we get 4d=12

⇒d=3

By substituting the value of d it in first equation, we get a=12

Therefore sum of first 17 terms in AP is

2

_ (2×12 + (30-1) × 3)

30

2

_ ×111

30

=7.4