Mathematics Class 7
A Tale of Three Intersecting Lines
Kinds of triangles, angle sums, which sides close, altitudes, and angles with a side.
15 lessons · ~83 min total
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Lessons in this topic
- 0 Start here Kinds of triangles, angle sums, which sides close, altitudes, and angles with a side. · 3 min You are here
- 1 Three lines that cross Three lines shut in a triangle, unless two are parallel or all three meet at one spot. · 5 min
- 2 Named by its sides Count the matching sides: three is equilateral, two is isosceles, none is scalene. · 5 min
- 3 Named by its angles The widest corner names the triangle: acute, right or obtuse. · 5 min
- 4 The three angles come to 180° The three angles of a triangle add to 180°. · 6 min
- 5 Two angles decide the third The third corner is 180° minus the two you know. · 5 min
- 6 The angle that leans out An exterior angle equals the two far corners added. · 6 min
- 7 Will these three close? Three lengths close into a triangle when each is less than the other two added. · 6 min
- 8 Longest side, widest corner The longest side is across from the widest corner. · 5 min
- 9 Direct road, roundabout road A road with a bend is longer than the direct road. That decides which sides close. · 7 min
- 10 The height from a corner An altitude drops straight from a corner to the opposite side, which may need extending. · 7 min
- 11 Two angles and the side between Two angles at the ends of a side make a triangle when they add to less than 180°. · 7 min
- 12 Checkpoint: roads, altitudes and rays A quick graded check on which sides close, altitudes, and two angles with a side. · 5 min
- 13 The big picture Eleven ideas on one screen. · 3 min
- 14 Track quiz A cheat-sheet table and eleven questions, one per idea. · 8 min
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