don steward
mathematics teaching 10 ~ 16

Sunday, 15 March 2009


several people devised an interesting way of constructing an angle bisector and dropping a perpendicular in a meeting led by Steph Prestage and Pat Perks (then of Birmingham University)

to construct an angle bisector: draw two arcs from the start point (the intersection of the two lines)

draw the cross diagonals of the resulting isosceles trapezium (or trapezoid)

join this crossover point to the start point

this same device (drawing two arcs) can be adapted to 'drop a perpendicular' to a line from a given point

Pat and Steph stress a view that it is helpful to use full circles rather than just arcs when constructing loci - to aid understanding

thanks to Ed Southall

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