Question

Write the explicit formula that represents the geometric sequence-2, 8, -32, 128

Answer 1

Well,  since we know is a geometric sequence, we can always get the common ratio  of it by simply dividing one value by the one behind it... so let's do so, with say hmm -32 and 8  -32/8 = -4  <-- our common ratio

the first term is -2

$\bf n^{th}\textit{ term of a geometric sequence}\\\\ a_n=a_1\cdot r^{n-1}\qquad \begin{cases} n=n^{th}\ term\\ a_1=\textit{first term's value}\\ r=\textit{common ratio}\\ ----------\\ a_1=-2\\ r=-4 \end{cases}\implies a_n=-2(-4)^{n-1}$