Parallelograms – Properties   A parallelogram is a special type of a polygon. it is a quadrilateral with both pair of opposite sides are parallel. Properties 1. Opposite sides are equal.       Opposite sides, AB = CD and AC = BD 2. Opposite angles are equal.      Opposite angles are ∠A = ∠D and ∠B […]

Read More →

Given: Two triangles △ ABC and △ ABD are on same base (or equal bases) AB, and area of △ ABC and △ ABD are equal. Proof: CD ∥ AB Construction: Draw CE and DF perpendicular to AB.So DF is the height of △ ADB, and CE is the height of △ABC. CE perpendicular to AB and DF perpendicular to AB.Since, lines perpendicular to same line […]

Read More →

Two triangles on the same base (or equal bases) and between the same parallels are equal in area. Given: △ ABC and △ PBC are two triangles on same base (or equal bases) BC and between the same parallels, BC and AP. To prove: ar △ ABC = ar △ PBC Construction: Through B, draw BD ∥ CA intersecting PA produced at D, and […]

Read More →

 Rhombus – Definition – Properties Definition: A rhombus is a quadrilateral (closed shape, plane figure) with four straight sides that are equal length also opposite sides are parallel and opposite angles are equal. A rhombuses is a type of parallelogram. All rhombuses are parallelograms, but not all parallelograms are rhombuses.  All squares are rhombuses, but not all […]

Read More →

Theorem – The line segment joining the mid-points of two sides of a triangle is parallel to the third side. Given: A triangle △ABC, in which D and E are mid points of sides AB and AC respectively. DE is joined. To prove: Line joining the mid points D and E (DE) is parallel to the third line […]

Read More →

 Theorem : In a parallelogram, opposite angles are equal.  Given: A parallelogram ABCD,  opposite sides of parallelogram are                         side AB and side DC                         side AD and side BC. To prove: Opposite angles of parallelogram are equal. […]

Read More →

 Elements of a Parallelogram In figure a Parallelogram ABCD.  There are four sides AB, BC, CD and DA and four angles ∠A, ∠B, ∠C and ∠D in a Parallelogram. AB and DC are opposite sides, and AD and BC are another pair of opposite sides. ∠A and ∠C are a pair of opposite angles, and another pair of opposite angles are ∠B and ∠D. AB […]

Read More →

Parallelograms on the same base and between the same parallels are equal in area. Given: Two parallelograms ABCD and EFCD, are on the same base DC and between the same parallel lines AF and DC. To prove: area (∥gm ABCD) = area (∥gm EFCD) Proof: In △ AED and △ BFC BC ∥ AD and AF is a transversal.So, ∠DAE = ∠CBF …..(1) (Corresponding angles of […]

Read More →

A diagonal of a parallelogram, divides it into two congruent triangles. Given: A parallelogram ABCD and AC is a diagonal, the diagonal AC divides parallelogram ABCD into two triangles △ ABC and △ CDA. To prove: These triangles △ ABD and △CDA are congruent,                        △ ABC ≅ △ CDA Proof: In △ ABC and △ CDA BC ∥ AD and AC […]

Read More →

If each pair of opposite sides of a quadrilateral is equal, then it is a parallelogram.  Given: ABCD is a quadrilateral, each pair of opposite sides of quadrilateral ABCD are AB and CD and also sides AD and BC are equal. AB = CD BC = AD To prove: ABCD is a parallelogram. Construction: Join A to C that is AC, is […]

Read More →