Question

find whether -150 the term of the AP 17, 12,7,2,4,...

Answer 1

Yes it is in the term of an given Ap

Answer 2

$an = a + (n - 1)d \\ d = a2 - a1 = 7 - 12 = - 5 \\ 12 + (150 - 1)( - 5) \\ 12 + 149 \times ( - 5) \\ 12 - 745 = - 733$