25 ! find first differences for the sequence in order from a1 to a5. determine whether or not the series is quadratic or not. -1, -3, -1, 5, 15 a) 2, 2, 6, 10; not quadratic b) 2, 2, 6, 10; quadratic c) -2, 2, 6, 10; not quadratic d) -2, 2, 6, 10; quadratic