# G.1.19.2 That Can’t Be Right, Can It?

- Author:
- Katie Akesson

Here is a figure where ray *r* meets line *l*. The dashed rays are angle bisectors.
Diego made the conjecture: “The angle formed between the angle bisectors is always a right angle, no matter what the angle between *r* and *l* is.”
It is difficult to tell specifically which angles Diego is talking about in his conjecture. Here is a labeled diagram and a rephrasing of Diego's conjecture with more specific details:

- We're given that ray
*CE*bisects angle*ACD*into two congruent angles that each measure*a*degrees. - We're given that ray
*CF*bisects angle*DCB*into two congruent angles that each measure*b*degrees. - Diego concludes that angle
*ECF*is a right angle, in other words*a*+*b*= 90 degrees.

Now it's your turn to practice creating a detailed, labeled diagram and rephrasing a conjecture.
Here are 2 intersecting lines that create 2 pairs of vertical angles:
This is a picture of 2 lines that cross, but we can't discuss the lines becaue there are no labels to refer to.
Use the tools below to create a

*diagram similar to the one above.***labeled**Priya writes the conjecture "Vertical angles are congruent". Rephrase Priya's conjecture more precisely using the labels from your diagram above.

Use **180 degree rotations** and your labeled diagram and detailed description to explain why Priya's conjecture is true.