proof for basic proportionality theorem
BPT(Thales Theorem) -
Given - In triangle ABC, DE is parallel to BC. DE bisects AB at D and AC at E.
To Prove - AD/BD= AE/CE
Construction - Join BE and CD and draw EF is perpendicular to AB and DG is perpendicular to AC.
As, EF is perpendicular to AB, EF is the height of tr's ADE and DBE.