BPT
Basic Proportionality Theoram
A line parallel to a side of the triangle intersects remaining sides in two distinct points, then it divides remaining sides in proportion.
Converse of BPT
If a line divides any two sides of a triangle in the same ratio, then the lineis parallel to the third side.
Tests of similarity.
Theoram of three parallel lines and their transversal.
The ratio of the intercepts made on a transversal by three parallel lines is equal to the ratio of corresponding intercepts made on any other transversal by the sake parallel lines.