H1. Triangles and trig : Similarity of triangles.
There are many different kinds of triangles, for
example, isoscles, equilateral, scalene, right-angled, acute-angled and
obtuse-angled.
Two triangles are said to be similar if all their sides are in a fixed
ratio. This will be true of any two triangles where one is an enlargement of
the other. These three triangles are all similar to each other:
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The sides in any two similar triangles are in a fixed
ratio. In the diagram, AB:DE=BC:EF=AC:DF
Or, you could write these ratios as fractions:
AB=BC=AC
DE EF DF
You can also compare sides within each triangle:
BC=EF
AC DF
AB=DE
AC DF
AB=DE
BC EF
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Drag some of
the points. The triangles remain similar. |
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