Question

for an arithmatic progression a=1 and d=4 what is the value of r if tn=81​

Answer 1

Answer:

The answer will be 21.

Step-by-step explanation:

We have given;

                         a = 1;

                        d = 4;

                        tn = 81;

For this the formula we apply will be;

                      an(tn) = a + d (n - 1);

Hence, we put the values in their respective variables of the formula;

                      81 = 1 + (4)(n - 1);

                       80 = 4n - 4;

                       84 = 4n;

                      n = 21;

Hence, the value of n (no. of terms) = 21.

That's all.