Stage: 5 Challenge Level: 
Why do this problem?
It calls for constructing your own equation from the information given and then solving it by a numerical method (e.g.interval halving or the Newton Raphson method.)
Key question
When solving an equation $f(a) = 0$ can we find values of $a$ for which the function is positive and values for which the function is negative?
Long problems. Circles. Similarity. Newton Raphson Method. Approximate solution by numerical methods.. Pythagoras' theorem. Scale factors. Golden ratio. Stage 5 needs dealing with. Other equations.
Published January 2000.
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