In this ten-minute video clip, Sal Khan, of Khan Academy, compares perpendicular bisectors to angle bisectors to medians to altitudes in this review. (09:56)

Salman Khan talks about scalene, isosceles, and equilateral triangles during this five-minute video. He also demonstrates that if you know the measure of two angles in a triangle, you can figure out the measurement of the third angle.

From pbslearningmedia.org, produced by Math Active

First it is established that triangles have sides and are measured by interior angles. They belong to categories based on that. The acute triangle is defined, illustrated and explained. There are many exercises helping students remember the attribute...s of Acute triangles as distinguishable from other triangles. Students will use an interactive protractor for practice to correctly measure interior angles to distinguish acute triangles from others.[more]

The instructor uses computer software to discuss vertical angles, exterior angles, alternate interior angles, etc. The sound quality could be a little better.

The instructor uses an electronic blackboard with different colors. The angle game is explained and played using a star shape. Using information student knows about various angles they can figure out the sizes of the angle X. Video can be stopped a...nd then restarted to get solution. Video gives some measurements and instructed to find the rest of the angles. This game and shape is definitely a challenge to students, but could be fun for students looking for extra practice on angle measurement. (09:49)[more]

In this brief lesson using a whiteboard, students learn to classify triangles as acute (all angles acute), right (one angle right), or obtuse (one angle obtuse). Students also learn that the sum of the measures of the angles of a triangle is 180 degr...ees, and students are asked to use this formula to find the measures of missing angles in given triangles. (00:52)[more]

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