Question

For an A.P if a=1 d=4 what is the value of n if tn=81.​

Answer 1

Step-by-step explanation:

a=t1=1

d=4

tn=a+(n-1)d

81=1+(n-1)4

81=1+4n-4

81=-3 + 4n

81+3 =4n

84=4n

84/4=n

21=n

n=21