Lesson 1 of 15
Three lines that cross
Show on a big screenPush one bamboo pole with your foot. The gap in the middle changes shape. Does it always stay a triangle?
Step 1 of 4
- Two lines cross. One corner.
- A third line cuts both. Three corners, one triangle.
- Two lines run parallel instead. One corner goes missing.
- All three lines pass through one spot. The three corners are one point.
Three lines, two ways to fail
Not always. Three lines cross in pairs. Each pair meets at one corner. The three corners make a triangle.
Two things can spoil the triangle. Two parallel lines never meet, so a corner is missing. Or all three lines pass through one spot. Then the three corners are one point.
Turn the third line. Find where the triangle disappears.
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