Stage: 5 Challenge Level: 
A triangle PQR, right angled at P, slides on a horizontal floor
with Q and R in contact with perpendicular walls. What is the locus
of P?
Circle theorems. alphas. epsilons. Quadrilaterals. Mathematical reasoning & proof. Manipulating algebraic expressions/formulae. Summation of series. Stage 5 - Reviewed 2012. Visualising. Loci.
Published September 1999.
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