we know that
arithematic sequence will always have common difference
(a)
−5, −7, −10, −14, −19, …
we can see that
they are not equal
so, this is not arithematic sequence
(2)
1.5, −1.5, 1.5, −1.5, …
we can see that
they are not equal
so, this is not arithematic sequence
(3)
4.1, 5.1, 6.2, 7.2, …
we can see that
they are not equal
so, this is not arithematic sequence
(4)
−1.5, −1, −0.5, 0, …
we can see that
they are equal
so, this is arithematic sequence