Mon Prof Augmenté
Parallel Lines Cutting Two Lines
Age 14 · Maths
Two straight lines cross at a point. Two parallel lines cut across them and form two triangles; each side of one triangle is the same multiple of its matching side in the other triangle.
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In the picture
- The crossing point: the shared vertex of both triangles
- The upper orange rod: the base of the upper triangle
- The lower orange rod: the base of the lower triangle
- The upper blue side: a side of the upper triangle from the crossing to the upper orange rod
- The lower blue side: the matching side of the lower triangle from the crossing to the lower orange rod
Examples
- A projector makes a small picture and a large screen picture with all matching sides scaled by the same factor.
- A tree and its shadow: the height and shadow length stay in the same ratio when sunlight rays are parallel.
Key takeaways
- Parallel lines cutting two crossing lines make two triangles with the same shape.
- Matching sides of those triangles are always in the same ratio.
Quiz: Parallel Lines Cutting Two Lines (Age 14)
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When two parallel lines cut across two lines that cross each other, what do they make?
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For the two triangles made by the parallel lines, how are matching sides related?
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Which point is the shared vertex of the two triangles in this configuration?
The answers, each with its explanation, are in the app. This lesson has left the free week, so its quiz is part of the subscription.
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