G.GCO.9 Isosceles 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!