In mathematics, a geometric progression, also known as a geometric sequence, is a sequence of numbers where each term after the first is found by multiplying the previous one by a fixed non-zero number called the common ratio. For example, the sequence 2, 6, 18, 54, ... is a geometric progression with common ratio 3. Similarly 10, 5, 2.5, 1.25, ... is a geometric sequence with common ratio 1/2. The sum of the terms of a geometric progression is known as a geometric series.
Thus, the general form of a geometric sequence is
and that of a geometric series is
where r ≠ 0 is the common ratio and a is a scale factor, equal to the sequence's start value. - Wikipedia.
to find common ratio, divide your second term by the first term. or divide your third term by your second term and so on..
thus, r = -8/-16 = -4/-8 = -2/-4 = -1/-2 = 1/2.
now that you have your common ratio r and your first term a,
the formula for geometric progression is
now your a=-16 and r=1/2
so the expression for the general term for this geometric progression is
same goes for question b c and d..and question 2 too!