Q. Write an explicit formula that represents the sequence defined by the following recursive formula:a1=1 and an=−2an−1Answer: an=
Identify Pattern: The recursive formula given is an=−2an−1, with the initial condition a1=1. To find the explicit formula, we will look at the first few terms of the sequence to identify a pattern.
Calculate a2: First, we calculate a2 using the recursive formula:a2=−2a1=−2(1)=−2.
Calculate a3: Next, we calculate a3:a3=−2a2=−2(−2)=4.
Calculate a4: Now, we calculate a4:a4=−2a3=−2(4)=−8.
Geometric Sequence: We can see that each term is −2 times the previous term. This is a geometric sequence with the first term a1=1 and a common ratio r=−2. The explicit formula for a geometric sequence is an=a1×r(n−1).
Substitute Values: Substituting the values of a1 and r into the formula, we get:an=1×(−2)n−1.
Final Explicit Formula: Simplifying the formula, we have the explicit formula for the sequence: an=(−2)n−1.
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