# G.GCO.9 Isosceles Triangles

- Author:
- Dan Dale, Tim Brzezinski

- Topic:
- Angles, Isosceles Triangles, Triangles

Interact with the applet below for a few minutes.
Then, answer the questions that follow.

*Be sure to change the locations of the white points and gray point each time before you re-slide the slider!***Questions:**1) Notice how the the triangle was constructed by constructing the

**green angles**first.

**What is true about the green angles?**2)

**What else did you notice about this triangle? Explain.**3) Fill in the blanks in the statement below to construct a true statement: If

**two __________________ of a triangle are _______________,**then

**the ______________**opposite

**those __________________**

**are also _________________.**4) Construct a formal 2-column (or paragraph) proof of the statement in (3).

*You may need to draw an auxiliary segment (or ray) within your diagram!*