Question

For an A. P., a = 1 and d = 4 . What is the value of n, if tn = 81 ? (10th standatd question is this. The chapter name is :- Aritimetic progression ) plzz ans the question and who will give right ans i will give him/her 5 stars!!!!

Answer 1

Given,

For an AP, a = 1

d = 4

tn = 81

To find,

The value of n.

Solution,

The value of n will be 21.

We can easily solve this problem by following the given steps.

According to the question,

For an AP, a (the first term) = 1

d (common difference) = 4

tn (nth term) = 81

We know that the formula to find the nth term for an Arithmetic Progression is given as follows:

tn = a+(n-1)d

Putting the values of tn, a and d,

81 = 1+(n-1)4

81 = 1+4n-4

81 = 4n-3

4n-3 = 81

4n = 81+3 (Moving 3 from the left-hand side to the right-hand side results in the change of the sign from minus to plus.)

4n = 84

n = 84/4

n = 21

Hence, the value of n is 21.