What are the riddles about triangles?

1, 80-year-old grandfather walks. Interpretation: Tripod walking, homophonic triangle

2. A city in the southeast and northwest, to whom is the southeast given? Explanation: Four corners and one corner are triangles.

This square is diagonally tangent. Interpretation: The diagonal of the four corners cuts a triangle.

4. Three sides plus three sides equals four sides. Interpretation: Two triangles are spliced into a quadrilateral.

5, three heads, sharp corners, we can't learn less.