After the Warm-Up, we discussed how you would show that a quadrilateral is a certain type on the coordinate plane. For example, if you think a quadrilateral is a rectangle, you would have to show that all of the angles are right angles. To show this you would show that all of the connected sides are perpendicular, which means you would have to show that their slopes are opposite reciprocals.
We worked on this worksheet: classifying-special-quads-on-the-coordinate-plane
The example below goes over what showing this work looks like. Here, we want to show the shape is an isosceles trapezoid, so you want to show that one pair of sides are parallel (have the same slope) and the other pair of sides are congruent (have the same length).
Lastly, many students had trouble with the proofs on p. 213 in the SpringBoard book, so we showed what it looks like to prove a property of a parallelogram. Note: We start with the given info that we have a parallelogram, and the other thing we need to do at the beginning of the proof is Create a line segment that splits the shape into two triangles that can be shown to be congruent. Once we show those triangles are congruent, we can then use CPCTC to say what we want about the shape.