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Write an explicit formula that represents the sequence defined by the following recursive formula:

a_(1)=80" and "a_(n)=-(1)/(4)a_(n-1)
Answer: 
a_(n)=

Write an explicit formula that represents the sequence defined by the following recursive formula:\newlinea1=80 and an=14an1 a_{1}=80 \text { and } a_{n}=-\frac{1}{4} a_{n-1} \newlineAnswer: an= a_{n}=

Full solution

Q. Write an explicit formula that represents the sequence defined by the following recursive formula:\newlinea1=80 and an=14an1 a_{1}=80 \text { and } a_{n}=-\frac{1}{4} a_{n-1} \newlineAnswer: an= a_{n}=
  1. Identify Pattern: To find the explicit formula for the sequence, we start by looking at the first few terms to identify a pattern. We know the first term is a1=80a_{1} = 80.
  2. Find Second Term: Now we apply the recursive formula to find the second term: a2=14a1=14×80=20a_{2} = -\frac{1}{4}a_{1} = -\frac{1}{4} \times 80 = -20.
  3. Find Third Term: Next, we find the third term using the recursive formula: a3=(14)a2=(14)×(20)=5a_{3} = -\left(\frac{1}{4}\right)a_{2} = -\left(\frac{1}{4}\right) \times (-20) = 5.
  4. Find Fourth Term: We continue this process to find the fourth term: a4=14a3=14×5=1.25a_{4} = -\frac{1}{4}a_{3} = -\frac{1}{4} \times 5 = -1.25.
  5. Determine Geometric Sequence: From these calculations, we can see that each term is 14-\frac{1}{4} times the previous term. This is a geometric sequence with the first term a1=80a_{1} = 80 and a common ratio r=14r = -\frac{1}{4}.
  6. Apply Explicit Formula: The explicit formula for a geometric sequence is given by an=a1×r(n1)a_{n} = a_{1} \times r^{(n-1)}. Substituting the values we have, we get an=80×(14)(n1)a_{n} = 80 \times (-\frac{1}{4})^{(n-1)}.

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