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 […]

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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 […]

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 In a parallelogram opposite sides are equal.  Given: A parallelogram ABCD, each pair of Opposite sides of parallelogram are side AB and side DC and side AD and side BC. To prove: Opposite sides of parallelogram are equal that is AB = DC    and    AD = BC  Construction: Join A to C that is AC, is a diagonal, the diagonal AC […]

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If two Lines are parallel to a third line then the lines are parallel to each other. Given: It is given that three lines l, m, and n, and line l ∥ line m and line m ∥ line n. To Prove:    Line l ∥ Line n Proof: Let us draw a line p transversal for lines l, m, and n. For lines l […]

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Angle Formed By Two Lines and a Transversal  In above figure line l, intersects two lines m and n at the point p and q respectively. Therefore, line l is a “Transversal” for lines m and n. Four angles are formed at the points p, by line l, name of these angles as  ∠1, ∠2, ∠3, and ∠4. Four angles are formed […]

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If the diagonals of a Quadrilateral, bisect each other then that Quadrilateral is a Parallelogram Given: ABCD is a quadrilateral with AC and BD are diagonals and diagonals intersect each other at O. i.e. OA = OC and OB = OD To Prove: ABCD is a parallelogram. Proof: In △AOD and △COB           […]

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