Given: ABCD is a parallelogram with AB parallel to CD and AD parallel to BC. Diagonal AC is congruent With your partner, you will work backwards from the statement to the proof until you feel confident that
D
to diagonal BD.
Prove: ABCD is a rectangle (angles A, B, C, and D are right angles).
you can prove that ABCD is a rectangle using only the given information.
Start with this sentence: I would know ABCD is a rectangle if I knew
Then take turns saying this sentence: I would know [what my partner just said] if I knew
Write down what you each say. If you get to a statement and get stuck, go back to an earlier statement and
try to take a different path.