Question

given a=5, n=15, sn=390, find d

Answer 1

Answer:

here's your answer

it is given that

a=5 , n=15 , sn =390

so by applying formula for calculating the sum is

n/2 ( 2a + ( n-1 )d ) we get ,

1/2( 10 + 14d ) = 26

10 + 14d = 52

14d = 42 and d =3 ans

Hope it helps