Question

t15=30,t20=50,S17=?if it is a A.P​

Answer 1

Step-by-step explanation:

Given:

1. t15=> a+14d=30.----(1)
2. T20=> a+19d=50----(2)

To find: A.P.

By (2)-(1):

=> a+19d-(a+14d)=50-30

a> a+19d-a-14d=20

=> 5d=20

=> d=20/5

=> d=4.-----(3)

(3) in (1):

=> a+14(4)=30

=> a=30-56

=> a=-26.

The A.P is -26,-22,-18,-14.........