Question

These are the first six terms of a sequence starting with a1 = 80:

80, 40, 20, 10, 5, 5/2, ….
Find a recursive formula for this sequence that is valid for n > 1.
Write your answer in simplest form.
an=?

Answer 1

Answer:

$a _{n} = a( {r}^{n - 1} ) \\ a _{n} = 80(2 {}^{n - 1} ) \\ a _{n} = \frac{80. {2}^{n} }{ {2}^{ 1} } \\a _{n} = 40( {2}^{n} ) \\ a _{n} = ( {2}^{3} \times 5)( {2}^{n} ) \\ a _{n} = 5( {2}^{n + 3} )$