SOLUTION: What are the first four terms of the following sequence: an = (-3)^n for n ≥ 1? A) 0, -3, 18, -81 B) -3, 18, -81, 324 C) 3, 18, 81, 324 D) 18, -81, 324, -1215

We begin by plugging in 1 for n:


   <-- so the only possible correct choice 
so far is C, for none of the others have 1st term -3

But to make sure, let's plug in 2 for n:




Uh oh!  Something's wrong!  The second term has to be 9, and
none of the choices have 2nd term 9.

Let's see what the correct answer would have to be.

Let's plug in 3 for n:


  

Let's plug in 4 for n:




So the correct answer is

-3, 9, -27, 81

So it's none of those listed.

Edwin