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'Isosceles Triangles' printed from http://nrich.maths.org/
This question is about isosceles triangles with an area of 9 cm$^2$.
One of the vertices must be at the point (20, 20).
Each vertex of the triangle must be at a grid point of a square grid,
so all the vertices will have whole number coordinates.
How many different triangles satisfy these four conditions?
Can you explain how you know that you have found them all?
Try to find them all. You may wish to use the GeoGebra applet below.
Click here for a poster of this problem