Parallel Lines Across a Triangle

In the picture

1. 1A line parallel to one side of the triangle
2. 2The short piece of the left side, above the parallel line
3. 3The short piece of the right side, above the parallel line
4. 4A crossing point where two lines meet, with parallel lines cutting all four rays

Examples

• Scaling a photo on a screen keeps every edge in the same ratio.
• A ladder leaning on a wall: each rung cuts the two rails in the same proportion.

Quiz: Parallel Lines Across a Triangle (Age 14)

1. 1

   A line is drawn parallel to one side of a triangle and cuts the other two sides. What does it do to those two sides?

   • It makes them perpendicular to each other.
   • It cuts them into equal pieces.
   • It cuts them in the same ratio.
2. 2

   When a line parallel to one side forms a small triangle inside a larger triangle, how are the sides of the two triangles related?

   • Their corresponding sides are proportional.
   • Their corresponding sides have no fixed relationship.
   • Their corresponding sides are always equal.
3. 3

   In the configuration where two lines cross and parallel lines cut all four rays, which statement matches the rule?

   • Only the two longest rays keep a ratio.
   • The pieces on the four rays keep the same ratio.
   • All pieces on the four rays become equal.

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.