Area of a figure is a number (in some unit) associated with the part of the plane enclosed by that figure. Two congruent figures have equal areas but the converse need not be true.
If a planar region formed by a figure T is made up of two non-overlapping planar regions formed by figures P and Q, then ar(T) = ar(P) + ar(Q), where ar(X) denotes the area of figure X.
Two figures are said to be on the same base and between the same parallels, if they have a common base (side) and the vertices, (or the vertex) opposite to the common base of each figure lie on a line parallel to the base. Parallelograms on the same base (or equal bases) and between the same parallels are equal in area.
Area of a parallelogram is the product of its base and the corresponding altitude. Parallelograms on the same base (or equal bases) and having equal areas lie between the same parallels.
If a parallelogram and a triangle are on the same base and between the same parallels, then area of the triangle is half the area of the parallelogram.
Triangles on the same base (or equal bases) and between the same parallels are equal in area.
Area of a triangle is half the product of its base and the corresponding altitude. Triangles on the same base (or equal bases) and having equal areas lie between the same parallels.
A median of a triangle divides it into two triangles of equal areas.