Final answer:
To find the seventh term of the geometric sequence 1, −3, 9, −27, ..., we calculate the common ratio and use it in the formula for the n-th term. The common ratio is −3 and the seventh term turns out to be 729. So the correct option is E.
Step-by-step explanation:
Calculating the SEVENTH Term of a Geometric Sequence
The given geometric sequence is 1, −3, 9, −27, ... and we are asked to find the seventh term. In a geometric sequence, each term after the first is found by multiplying the previous term by a constant called the common ratio (r). To find the common ratio, we can divide the second term by the first term, or the third term by the second term, and so on.
Common ratio (r) calculation:
Divide the second term (−3) by the first term (1), which gives us r = −3.
To find the seventh term, we use the formula for the n-th term of a geometric sequence, which is:
a_n = a_1 × r^(n-1), where a_n is the n-th term, a_1 is the first term, and n is the term number.
Seventh term calculation:
a_7 = 1 × (−3)^(7-1) = 1 × (−3)^6. Since −3 to an even power is positive, the answer is 1 × 3^6 = 729.
Therefore, the seventh term of the geometric sequence is 729.