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

a_(1)=100" and "a_(n)=-(1)/(5)a_(n-1)
Answer: 
a_(n)=

Write an explicit formula that represents the sequence defined by the following recursive formula:\newlinea1=100 and an=15an1 a_{1}=100 \text { and } a_{n}=-\frac{1}{5} 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=100 and an=15an1 a_{1}=100 \text { and } a_{n}=-\frac{1}{5} a_{n-1} \newlineAnswer: an= a_{n}=
  1. Identify Pattern: To find an explicit formula for the sequence, we start by looking at the first few terms to identify a pattern.\newlineGiven a1=100a_{1}=100, we can find a2a_{2} using the recursive formula an=15an1a_{n}=-\frac{1}{5}a_{n-1}.\newlinea2=15a1=15×100=20a_{2} = -\frac{1}{5}a_{1} = -\frac{1}{5} \times 100 = -20
  2. Calculate a2a_{2}: Next, we find a3a_{3} using the same recursive formula.a3=15a2=15×(20)=4a_{3} = -\frac{1}{5}a_{2} = -\frac{1}{5} \times (-20) = 4
  3. Calculate a3a_{3}: We continue this process to find a4a_{4}.\newlinea4=15a3=15×4=0.8a_{4} = -\frac{1}{5}a_{3} = -\frac{1}{5} \times 4 = -0.8
  4. Find a4a_{4}: From the pattern, we can see that each term is 15-\frac{1}{5} times the previous term. This is a geometric sequence with the first term a1=100a_{1} = 100 and common ratio r=15r = -\frac{1}{5}. The explicit formula for a geometric sequence is an=a1r(n1)a_{n} = a_{1} \cdot r^{(n-1)}. Substituting the values we have, we get an=100(15)(n1)a_{n} = 100 \cdot (-\frac{1}{5})^{(n-1)}.

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