Stage: 5 Short Challenge Level: 
Test the result for several small values of $n$ and try to decide why the absolute value appears in the formula.
What values of $n$ are you asked to prove the result for and what method of proof does this suggest?
Fibonacci sequence. Powers & roots. Mathematical induction. Quadratic equations. Golden ratio. Continued fractions. Making and proving conjectures. Binomial Theorem. epsilons. Surds.
Published November 2009,December 2009.
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