The formula for an is: a_n=2•(-4)^(n-1)
The explicit formula for the nth term in a GEOMETRIC sequence is: a_n = a_1 * r^(n-1)
Wherein a_1 = first term in the sequence, a_n = nth term in sequence, r = common ratio between terms, n = # of term in the sequence being found (also means that n-1 is the # for the previous term).
In sequence 2, -8, 32…
We know that 2 is the FIRST term, or a_1.
What about r? Well,
2(r)= -8
2(-4) = -8, so r = -4.
-8(-4)= 32;
32(-4)= -128;
-128(-4)= 512;
512(-4)= -2048;
…And so on.
Substitute knowns into the formula:
a_n= 2*(-4)^(n-1)
Or
a_n= (-1/2)*(-4)^n
But I would go with the first one as an answer.
Here’s a picture of the work if it helps to see (I’m on my phone so it’s harder to type out the formulas):
Hope this helps!