https://www.khanacademy.org/math/geometry/hs-geo-congruence/hs-geo-quadrilaterals-theorems/v/proof-opposite-sides-of-parallelogram-congruent 2021-02-16T16:08:12Z Proof: Opposite sides of a parallelogram Sal proves that a figure is a parallelogram if and only if opposite sides are congruent. Sal Khan video https://cdn.kastatic.org/googleusercontent/Aou3bes2NVoI_9-pt3FpYxyQjlLKBzk0bwXJZq0kKq94M8q29PBoRIhR6V-0z3AOc8Kl9JWtlmC8n0yfJP3JZJQ Proof: Opposite sides of a parallelogram Sal proves that a figure is a parallelogram if and only if opposite sides are congruent. https://cdn.kastatic.org/ka-youtube-converted/LhrGS4-Dd9I.mp4/LhrGS4-Dd9I.mp4 510 Missing angles of polygons https://www.khanacademy.org/math/cc-fourth-grade-math/plane-figures/imp-classifying-geometric-shapes/a/quadrilaterals-review 2021-06-30T20:49:30Z Quadrilaterals review Review the following quadrilaterals: parallelogram, trapezoid, rhombus, rectangle, and square.  Then, try some practice problems. article https://www.khanacademy.org/math/geometry/hs-geo-congruence/hs-geo-quadrilaterals-theorems/v/proof-diagonals-of-a-parallelogram-bisect-each-other 2021-02-16T16:08:12Z Proof: Diagonals of a parallelogram Sal proves that a quadrilateral is a parallelogram if and only if its diagonals bisect each other. Sal Khan video https://cdn.kastatic.org/googleusercontent/BoWcWWoNIz6F-yhntRfgBQ16ESP1UFJk_C7gy5uwM6rrCwhcWmf0FcNBsncukkUxi-8eOJOwhbE-pNA3h4-UawCz Proof: Diagonals of a parallelogram Sal proves that a quadrilateral is a parallelogram if and only if its diagonals bisect each other. https://cdn.kastatic.org/ka-youtube-converted/TErJ-Yr67BI.mp4/TErJ-Yr67BI.mp4 546 Missing angles of polygons https://www.khanacademy.org/districts-courses/geometry-scps-pilot-textbook/x398e4b4a0a333d18:polygons-and-quadrilaterals/x398e4b4a0a333d18:properties-of-parallelograms/e/regular-polygons-advanced-8th 2026-04-07T23:17:37.123726494Z Diagonal properties of parallelogram Polygons advanced supriya exercise https://www.khanacademy.org/math/geometry/hs-geo-congruence/hs-geo-quadrilaterals-theorems/v/proof-opposite-angles-of-parallelogram-congruent 2021-02-16T16:08:13Z Proof: Opposite angles of a parallelogram Sal proves that opposite angles of a parallelogram are congruent. Sal Khan video https://cdn.kastatic.org/googleusercontent/6y9cgS_Ed8ofB7a7kabkdW7h8oxf3miLKnWKrP1ga4Us7tv5pMbOwfCP37w9HztilyNNuQKK2C0J_Slsai2VzgTd1g Proof: Opposite angles of a parallelogram Sal proves that opposite angles of a parallelogram are congruent. https://cdn.kastatic.org/ka-youtube-converted/oIV1zM8qlpk.mp4/oIV1zM8qlpk.mp4 248 Missing angles of polygons https://www.khanacademy.org/districts-courses/geometry-scps-pilot-textbook/x398e4b4a0a333d18:polygons-and-quadrilaterals/x398e4b4a0a333d18:properties-of-parallelograms/e/using-properties-basic-8th 2026-03-07T07:20:41.87360937Z Side and angle properties of a parallelogram (level 1) Side and angle properties of a parallelogram (level 1) supriya exercise https://www.khanacademy.org/math/geometry-home/geometry-shapes/angles-with-polygons/v/sum-of-interior-angles-of-a-polygon 2023-04-19T21:01:17.089483175Z Sum of interior angles of a polygon To find the interior angle sum of a polygon, we can use a formula: interior angle sum = (n - 2) x 180°, where n is the number of sides. For example, a pentagon has 5 sides, so its interior angle sum is (5 - 2) x 180° = 3 x 180° = 540°. Sal Khan video https://cdn.kastatic.org/googleusercontent/Dy9dwu-r7REqsvHnPJFG9BZyZgxZhkCsmdatuLMVhinf3RDOohVKv5QYloc5nPaMFXRcHpX97XgtX1-5mr9LXQ4xFA Sum of interior angles of a polygon To find the interior angle sum of a polygon, we can use a formula: interior angle sum = (n - 2) x 180°, where n is the number of sides. For example, a pentagon has 5 sides, so its interior angle sum is (5 - 2) x 180° = 3 x 180° = 540°. https://cdn.kastatic.org/ka-youtube-converted/qG3HnRccrQU.mp4/qG3HnRccrQU.mp4 550 Missing angles of polygons https://www.khanacademy.org/math/geometry-home/geometry-shapes/angles-with-polygons/v/sum-of-the-exterior-angles-of-convex-polygon 2023-05-12T21:01:01.897246564Z Sum of the exterior angles of a polygon Learn a simple and elegant way to find the sum of the exterior angles of any convex polygon. You will see how to redraw the angles adjacent to each other and form a circle. Then you will discover that the sum of the exterior angles is always 360 degrees. Watch this video to master this important skill in geometry. Sal Khan video https://cdn.kastatic.org/googleusercontent/UC5fok88ogGOHxPgpquz_lcohc8q7cIY62SWTfzzJQATMpf7mmAbqUGP8cAnBW4xbNhV7LmbjdYqHsqz0heaI7kf Sum of the exterior angles of a polygon Learn a simple and elegant way to find the sum of the exterior angles of any convex polygon. You will see how to redraw the angles adjacent to each other and form a circle. Then you will discover that the sum of the exterior angles is always 360 degrees. Watch this video to master this important skill in geometry. https://cdn.kastatic.org/ka-youtube-converted/W9B3VYdC5T8.mp4/W9B3VYdC5T8.mp4 324 Missing angles of polygons https://www.khanacademy.org/math/geometry-home/geometry-shapes/angles-with-polygons/e/angles_of_a_polygon 2026-03-24T23:41:07.080866137Z Angles of a polygon Find the sum of interior angles of different polygons. Sid Patel exercise