Question

15th teem of AP is 21 and the common difference is -3 ,then find the first term

Answer 1

Answer:

a15=21.

d=-3.

a=?.

an=a+(n-1)d.

a15=a+(15-1)(-3).

21=a+(14)(-3).

21=a+(-42).

21=a-42. (Because +×-=-).

21+42=a.

a=63.

I think this is your answer.