When does a parallelogram become a rectangle?
When all four internal angles become right angles.
A parallelogram has opposite sides parallel and equal, and its opposite angles equal, but its angles need not be 90°.
A rectangle is a special parallelogram in which every interior angle measures exactly 90°.
Since co-interior angles of a parallelogram are supplementary, once one angle is 90° all four automatically become 90°, giving a rectangle.
Equal adjacent sides give a rhombus, and perpendicular diagonals also describe a rhombus, not a rectangle.
Hence, the answer is when all four internal angles become right angles.
Important Questions from Geometry
ABCDEF is a regular hexagon. Side of the hexagon is 36 cm. What is the area of the triangle AOB ?
If ∆ABC ~ ∆DEF, and BC = 4 cm, EF = 5 cm and the area of triangle ABC = 80 cm 2, then the area of the triangle DEF is:
If Δ ABC is right angled at B, AB = 12 cm and ∠CAB = 60°, determine the length of BC.
If ΔABC and ΔDEF are congruent triangles, then which of the following is FALSE?
D and E are points on the sides AB and AC, respectively, of ΔABC such that DE is parallel to BC and AD ∶ DB = 7 ∶ 9. If CD and BE intersect each other at F. then find the ratio of areas of ΔDEF and ΔCBF.
