Question

WHAT IS COROLLARY HOW TO APPLY IT.
HOW THE RATIO.

Answer 1

COROLLARY : It is a prediction wich can be proved by a already proved theorem. 
For ex:
BPT theorem states that If a line is drawn parallel to one side of a triangle intersecting the other two sides, then it divides the two sides in the same ratio.
and corollary to this is,
if a triangle ABC, a line DE║BC, intersects AB in D and AC in E, then:
AB/AD = AC/AE

Hope u have understood the concept.............