Question

Is 105, a term of A.P. 1+4+7+11+........? ​

Answer 1

An = A + (n-1)D

d = 11-7 = 7-4 = 4-1 = 3

A = 1

put An = 105 in equation,

105 = 1 + 3(n-1)

104 = 3 (n-1)         {n is supposed to be a natural number}

104/3 is not a natural number so n-1 is not natural so n is not natural

SO 105 IS NOT A TERM OF THE AP