Q. Find the 13th term of the geometric sequence 1,−3,9,…Answer:
Identify Geometric Sequence: The given sequence is a geometric sequence, which means each term after the first is found by multiplying the previous term by a common ratio r. To find the 13th term, we need to identify the common ratio and use the formula for the nth term of a geometric sequence, which is an=a1×r(n−1), where an is the nth term, a1 is the first term, and r is the common ratio.
Find Common Ratio: We can find the common ratio by dividing the second term by the first term. So, r=1−3=−3.
Calculate 13th Term: Now that we have the common ratio, we can use the formula to find the 13th term. Plugging in the values, we get a13=1×(−3)13−1=1×(−3)12.
Calculate 13th Term: Now that we have the common ratio, we can use the formula to find the 13th term. Plugging in the values, we get a13=1×(−3)13−1=1×(−3)12. Calculating (−3)12, we get 531441, since (−3)12 means multiplying −3 by itself 12 times, and a negative number raised to an even power results in a positive number.
Calculate 13th Term: Now that we have the common ratio, we can use the formula to find the 13th term. Plugging in the values, we get a13=1×(−3)13−1=1×(−3)12. Calculating (−3)12, we get 531441, since (−3)12 means multiplying −3 by itself 12 times, and a negative number raised to an even power results in a positive number. Therefore, the 13th term of the sequence is a13=1×531441=531441.
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