Let's see if we can't be logical here......Pick a formula and see what it yields. For example, choose D.
For n = 1 ---> -1 x 4^1 ----> -1 x 4 = -4, when the correct value is 1. Therefore D is out.
Try C. For n = 1 ---> 1 x 4^(1-1) ---> 1 x 4^0 ----> 1 x1 ---> 1, So it is correct for n =1. How about
n=2? 1 x 4^(2-1) = 1 x 4^1 = 1 x 4 = 4, when the correct answer is -4. Therefore C is out
I'm sure you can do the remaining two choices....
