Question

how many terms are in this a.p 70,63,56,49....0. step by step​

Answer 1

Given:-

A.P. are is in the 70, 63, 56, 49..

Last term = 21

First term = 70

Common difference= (70-63) = -7

To find:-

Which term of the given A.P. is 21 = ?

Find:-

Let the first term be a and common difference be d and last term be l.

First term(a) = 70

Common difference(d) = (70-63)= -7

We know that,

L = a + (n-1)d

=>21= 70 + (n-1)(-7)

=>21 = 70 -7n+7

=>21 = 77- 7n

=>7n= 77-21

=>7n = 56

=>n = 8

Hence its 8th term will be 21.

Hope this will helpful for you

Answer 2

last term=first term+(n-1)d

n-1=(l-a)/d

n-1=(0-70)/-7

n-1=70/7

n-1=10

n=10+1

n=11