Question

Help plzzzz! pre calc question

Answer 1

`\sum^(\infty)_0 {(-3)^n}`

Explanation:

Notice that the series: 1 - 3 + 9 - 27 +... clearly has powers of the factor 3 in its terms and it is also an alternate series (the terms alternate from positive to negative). The terms are positive for
`a_0, a_2, a_4, ...` (even terms) , while the odd terms
`a_1, a_3, a_5, ...` are negative. (so most likely there should be a factor (-1) in the common ratio.

We can then represent it with the following summation expression:

`\sum^(\infty)_0 {(-3)^n}` given that each of its first four terms are:

`a_0=(-3)^0=1\\a_1=(-3)^1=-3\\a_2=(-3)^2=(-3)*(-3)=9\\a_3=(-3)^3=(-3)*(-3)*(-3)=-27`