Angles in similar triangles (8th grade math)
What is kind of amazing about similar triangles is that to show that two triangles are similar, it is sufficient to show that TWO (only two) of their angles are congruent. You don't need to check anything about the sides!
And, in similar triangles (as in all similar figures), the corresponding sides are in the same ratio (or proportional).
Once we have explored this principle, we solve an exercise that asks whether two triangles are similar or not.
The latter half of the video is spent solving another exercise where we need to use a proportion to find an unknown side length of a triangle.
See also
Angle sum of a triangle — video lesson
Math Mammoth Grade 8 curriculum
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