You have to closely look at the values and figure out a pattern.
If you look at the right-hand column, you can see a pattern of powers of 3.
3^0 = 1
3^1 = 3
3^2 = 9
3^3 = 27
3^4 = 81
But the "power" doesn't correspond with nth term.
For example, when we have the power of "1", it is "2nd term", a_2.
Also, when we have the power of "3", it is the "4th term", a_4.
Hence,
the pattern suggests us that
the power is "1 less than" the nth term. In other words, the formula can be "a_(n-1) to the power 3" to incorporate this.
Looking at the choices,
A is correct.
