Q. Write an explicit formula that represents the sequence defined by the following recursive formula:a1=7 and an=5an−1Answer: an=
Identify Base Case: Identify the base case and the recursive step from the given recursive formula.The base case is a1=7, which means the first term of the sequence is 7. The recursive step is an=5an−1, which means each term is 5 times the previous term. This indicates that the sequence is geometric with a common ratio of 5.
Write First Few Terms: Write the first few terms of the sequence using the recursive formula to observe the pattern.a1=7a2=5a1=5×7=35a3=5a2=5×35=175a4=5a3=5×175=875We can see that each term is 5 times the previous term, confirming that the sequence is geometric.
Derive Explicit Formula: Derive the explicit formula for the geometric sequence.For a geometric sequence, the nth term is given by an=a1⋅rn−1, where a1 is the first term and r is the common ratio. In this case, a1=7 and r=5. Therefore, the explicit formula is an=7⋅5n−1.
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