What is a theorem?
Definition of theorem:
A theorem is a statement to be proved either on the basis of axioms or on the basis of previous proved statements.
Examples:
Pythagoras Theorem: In a right-angled triangle, the square of the hypotenuse is equal to the sum of the squares of the other two sides.
Basic proportionality theorem: If a line is drawn parallel to one side of a triangle to intersect the other sides in distinct points, the other two sides are divided in the same ratio.