If the 9th term of an AP is five times the 5th term, find the relationship between a and d

Answer 1

The n’th term of an AP is a + (n − 1)d

The 5th term is:     a + 4d
The 9th term is:   a + 8d

9th term is five times 5th term. so, a + 8d = 5(a+4d)

a + 8d = 5a + 20d

4a = -12d

a = =3d

 

Comments

4a = - 12d

a = - 3d

a/d = - 3/1

a = -3d