1. 6. Show that consecutive angles are supplementary

2. What do you see? What Makes a Quadrilateral a Parallelogram? Are both pairs of opposite sides parallel?

3. Is one pair of opposite sides congruent and parallel? In This Picture…

4. Are both pairs of opposite sides congruent?

5. Are both pairs of opposite angles congruent? What is this Picture?

6. What is this?

8. Is a Pentagon a Parallelogram? NO!

9. GUIDED PRACTICE for Examples 2 and 3 What theorem can you use to show that the quadrilateral is a parallelogram? 3. Two pairs of opposite sides are equal. Therefore, the quadrilateral is a parallelogram. By theorem 8.7 ANSWER

10. GUIDED PRACTICE for Examples 2 and 3 What theorem can you use to show that the quadrilateral is a parallelogram? 4. By theorem 8.8, if the opposite angles are Congruent, the quadrilateral is a parallelogram. ANSWER

11. GUIDED PRACTICE for Examples 2 and 3 For what value of x is quadrilateral MNPQ a parallelogram? Explain your reasoning. 5. SOLUTION [ Diagonals in bisect each other ] By Theorem 8.6 2x =10 – 3x Add 3x to each side 5x =10 Divide each side by 5 x =2

12. 6. Show that consecutive angles are supplementary

13. Game Time: Name that Theorem

17. 6. Show that consecutive angles are supplementary

18. Game Time: Name that Theorem

19. EXAMPLE 4 Use coordinate geometry SOLUTION One way is to show that a pair of sides are congruent and parallel. Then apply Theorem 8.9. First use the Distance Formula to show that AB and CD are congruent. AB = = [2 – (–3)] 2 + (5 – 3) 2 29 CD = (5 – 0) 2 + (2 – 0) 2 = 29 Show that quadrilateral ABCD is a parallelogram.

20. EXAMPLE 4 Use coordinate geometry Because AB = CD = 29, AB CD. Then use the slope formula to show that AB CD. Slope of AB = 5 – (3) 2 – (–3) = 2 5 Slope of CD = 2 – 0 5 – 0 = 2 5 Because AB and CD have the same slope, they are parallel. AB and CD are congruent and parallel. So, ABCD is a parallelogram by Theorem 8.9. ANSWER

21. EXAMPLE 4 GUIDED PRACTICE for Example 4 6. Refer to the Concept Summary. Explain how other methods can be used to show that quadrilateral ABCD in Example 4 is a parallelogram. SOLUTION Find the Slopes of all 4 sides and show that each opposite sides always have the same slope and, therefore, are parallel. Find the lengths of all 4 sides and show that the opposite sides are always the same length and, therefore, are congruent. Find the point of intersection of the diagonals and show the diagonals bisect each other.

22. EXAMPLE 4 GUIDED PRACTICE for Example 4 = [-4 – (0)] 2 + (1 – 8) 2 = [4 – (8)] 2 + (-1 – 6) 2 65 DK = TA = D A T K DK and TA are congruent and parallel. So, TDKA is a parallelogram by Theorem 8.9.

23. In Conclusion…

24. Pg 526 # 1-3, 11-14 Don’t forget your homework.