Question

If the n'th term of the A.P, -1,4,9,14...is 129.find thevalue of n.

Answer 1

-1,4,9,14.......129

first term = a = -1

common difference = d = 4- (-1) = 4+1 = 5

n'th term = Tn = 129

number of terms = n = ?

Tn = a+(n-1)d

129 = -1+(n-1)5

129+1 = 5n -5

130+5 = 5n

135 = 5n

135/5 = n

27 = n