Question

Which term ap 21,18,15....,78?

Answer 1

Answer:

a=21,d=18-21=3,an=78

an=a+(n-1)d

78=21+(n-1)-3

78-21=(n-1)-3

57=(n-1)-3

(n-1)=57/3

(n-1)=19

n=19+1

n=20

Answer 2

Answer:

21,18,15,12,9,3

Step-by-step explanation:

reverse multiples of 3.