Prove by vector method that the parallelograms on the same base and between the same parallels are equal in area.

If a triangle and a parallelogram lie on the same base and between the same parallels, then prove that the area of the triangle is equal to half of the area of parallelogram.

Triangle ABC and parallelogram ABEF are on the same base, AB as in between the same parallels AB and EF. Prove that ar (DeltaABC) = 1/2 ar(|| gm ABEF)

Prove by vector method that the diagonals of a rhombus bisect each other at right angles.

Prove by vector method that an angle in a semi-circle is a right angle.

The angle between parallel vectors is

Prove by vector method that median to the base of an isoscels triangle is perpendicular to the base.

Prove by vector method that the perpendiculars (altitudes) from the vertices to the sides of a triangle are concurrent.

The angle between anti-parallel vectors is

Prove by vector method that cos(A+B)cos AcosB-sinAsinBdot