- Enlargement or Dilatation
- If DPQR is the image of DABC (Pre image) and K is the enlargement factor,
- If K = 1 the triangles are congruent.
- The ratio of their areas is K2
- (SAS similarity)
If a pair of corresponding angles are equal and the sides including them are proportional, the triangles are similar.
- (AA similarity)
If two pairs of corresponding angles are equal then the triangles are similar
- (SSS similarity)
If three pairs of corresponding sides are proportional, then the two triangles are similar.
- A perpendicular drawn from the right angle vertex of a right triangle to the hypotenuse divides the triangle into two triangles similar to each other and also to the original triangle.
- In DABC, if ÐA = 90o and AD ^ BC (D is the foot of the altitude)
AB2 = BC . BD, AC2 = BC . CD and AD2 = BD.CD
