equivalence relations in mathematics k 16
play

Equivalence relations in mathematics, K-16+ Art Duval Department of - PowerPoint PPT Presentation

Definitions and motivation Examples More theory Equivalence relations in mathematics, K-16+ Art Duval Department of Mathematical Sciences University of Texas at El Paso AMS Southeastern Sectional Meeting University of Louisville October 5,


  1. Definitions and motivation Examples More theory Equivalence relations in mathematics, K-16+ Art Duval Department of Mathematical Sciences University of Texas at El Paso AMS Southeastern Sectional Meeting University of Louisville October 5, 2013 Art Duval Equivalence relations in mathematics, K-16+

  2. Definitions and motivation Fractions Examples Geometry More theory Real life One reason fractions are hard 2 3 + 1 5 = Art Duval Equivalence relations in mathematics, K-16+

  3. Definitions and motivation Fractions Examples Geometry More theory Real life One reason fractions are hard 2 3 + 1 5 = 10 15 + 3 15 Art Duval Equivalence relations in mathematics, K-16+

  4. Definitions and motivation Fractions Examples Geometry More theory Real life One reason fractions are hard 2 3 + 1 5 = 10 15 + 3 15 = 13 15 Art Duval Equivalence relations in mathematics, K-16+

  5. Definitions and motivation Fractions Examples Geometry More theory Real life One reason fractions are hard 2 3 + 1 5 = 10 15 + 3 15 = 13 15 We have to use 2 3 = 10 15 and 1 5 = 3 15 . Art Duval Equivalence relations in mathematics, K-16+

  6. Definitions and motivation Fractions Examples Geometry More theory Real life One reason fractions are hard 2 3 + 1 5 = 15 + 3 10 15 = 13 15 We have to use 2 3 = 10 15 and 1 5 = 3 15 . Questions: Art Duval Equivalence relations in mathematics, K-16+

  7. Definitions and motivation Fractions Examples Geometry More theory Real life One reason fractions are hard 2 3 + 1 5 = 10 15 + 3 15 = 13 15 We have to use 2 3 = 10 15 and 1 5 = 3 15 . Questions: ◮ If 2 3 and 10 15 are equal, why can we use one but not the other? Art Duval Equivalence relations in mathematics, K-16+

  8. Definitions and motivation Fractions Examples Geometry More theory Real life One reason fractions are hard 2 3 + 1 5 = 10 15 + 3 15 = 13 15 We have to use 2 3 = 10 15 and 1 5 = 3 15 . Questions: ◮ If 2 3 and 10 15 are equal, why can we use one but not the other? ◮ Could we have used something else besides 10 15 ? Art Duval Equivalence relations in mathematics, K-16+

  9. Definitions and motivation Fractions Examples Geometry More theory Real life One reason fractions are hard 2 3 + 1 5 = 10 15 + 3 15 = 13 15 We have to use 2 3 = 10 15 and 1 5 = 3 15 . Questions: ◮ If 2 3 and 10 15 are equal, why can we use one but not the other? ◮ Could we have used something else besides 10 15 ? ◮ Would we use something else in another situation, or should we always use 10 15 ? Art Duval Equivalence relations in mathematics, K-16+

  10. Definitions and motivation Fractions Examples Geometry More theory Real life Equivalent fractions Definition: a b ∼ c d if they reduce to the same fraction ( ad = bc ). Art Duval Equivalence relations in mathematics, K-16+

  11. Definitions and motivation Fractions Examples Geometry More theory Real life Equivalent fractions Definition: a b ∼ c d if they reduce to the same fraction ( ad = bc ). It’s easy to check ∼ is an equivalence relation, Art Duval Equivalence relations in mathematics, K-16+

  12. Definitions and motivation Fractions Examples Geometry More theory Real life Equivalent fractions Definition: a b ∼ c d if they reduce to the same fraction ( ad = bc ). It’s easy to check ∼ is an equivalence relation, so we can partition fractions as follows: a b and c d are in the same part (“equivalence class”) if a b ∼ c d . 1 17 2 10 1 3 4 20 2 34 3 15 5 15 7 35 4 6 4 14 10 8 40 16 8 12 6 21 50 40 70 28 10 7 20 8 2 7 8 36 20 14 20 12 10 35 14 63 Art Duval Equivalence relations in mathematics, K-16+

  13. Definitions and motivation Fractions Examples Geometry More theory Real life Adding fractions (revisited) b ∼ c a if d e f ∼ g and h Art Duval Equivalence relations in mathematics, K-16+

  14. Definitions and motivation Fractions Examples Geometry More theory Real life Adding fractions (revisited) a b ∼ c if d f ∼ g e and h a b + e f ∼ c d + g then h Art Duval Equivalence relations in mathematics, K-16+

  15. Definitions and motivation Fractions Examples Geometry More theory Real life Adding fractions (revisited) a b ∼ c if d e f ∼ g and h a b + e f ∼ c d + g then h So, really we should say � 2 � � 1 � � 13 � + = 3 5 15 , because anything equivalent to 2 3 plus anything equivalent to 1 5 “equals” something equivalent to 13 15 . Art Duval Equivalence relations in mathematics, K-16+

  16. Definitions and motivation Fractions Examples Geometry More theory Real life Adding fractions (revisited) a b ∼ c if d e f ∼ g and h a b + e f ∼ c d + g then h So, really we should say � 2 � � 1 � � 13 � + = 3 5 15 , because anything equivalent to 2 3 plus anything equivalent to 1 5 “equals” something equivalent to 13 15 . ◮ But it’s hard to compute unless we pick the right representative. Art Duval Equivalence relations in mathematics, K-16+

  17. Definitions and motivation Fractions Examples Geometry More theory Real life Adding fractions (revisited) a b ∼ c if d f ∼ g e and h a b + e f ∼ c d + g then h So, really we should say � 2 � � 1 � � 13 � + = 3 5 15 , because anything equivalent to 2 3 plus anything equivalent to 1 5 “equals” something equivalent to 13 15 . ◮ But it’s hard to compute unless we pick the right representative. ◮ In other settings, we stick to the fraction in lowest terms, a distinguished representative. Art Duval Equivalence relations in mathematics, K-16+

  18. Definitions and motivation Fractions Examples Geometry More theory Real life Similarity, congruence, etc. Some equivalence relations from geometry: Art Duval Equivalence relations in mathematics, K-16+

  19. Definitions and motivation Fractions Examples Geometry More theory Real life Similarity, congruence, etc. Some equivalence relations from geometry: ◮ Similarity ◮ same “shape”, possibly different size ◮ can get via dilation, reflection, rotation, translation Art Duval Equivalence relations in mathematics, K-16+

  20. Definitions and motivation Fractions Examples Geometry More theory Real life Similarity, congruence, etc. Some equivalence relations from geometry: ◮ Similarity ◮ same “shape”, possibly different size ◮ can get via dilation, reflection, rotation, translation ◮ Congruence ◮ same “shape”, size ◮ can get via reflection, rotation, translation Art Duval Equivalence relations in mathematics, K-16+

  21. Definitions and motivation Fractions Examples Geometry More theory Real life Similarity, congruence, etc. Some equivalence relations from geometry: ◮ Similarity ◮ same “shape”, possibly different size ◮ can get via dilation, reflection, rotation, translation ◮ Congruence ◮ same “shape”, size ◮ can get via reflection, rotation, translation ◮ Same shape, size, chirality ◮ can get via rotation, translation Art Duval Equivalence relations in mathematics, K-16+

  22. Definitions and motivation Fractions Examples Geometry More theory Real life Similarity, congruence, etc. Some equivalence relations from geometry: ◮ Similarity ◮ same “shape”, possibly different size ◮ can get via dilation, reflection, rotation, translation ◮ Congruence ◮ same “shape”, size ◮ can get via reflection, rotation, translation ◮ Same shape, size, chirality ◮ can get via rotation, translation ◮ Same shape, size, chirality, orientation ◮ can get via translation Art Duval Equivalence relations in mathematics, K-16+

  23. Definitions and motivation Fractions Examples Geometry More theory Real life Similarity, congruence, etc. Some equivalence relations from geometry: ◮ Similarity ◮ same “shape”, possibly different size ◮ can get via dilation, reflection, rotation, translation ◮ Congruence ◮ same “shape”, size ◮ can get via reflection, rotation, translation ◮ Same shape, size, chirality ◮ can get via rotation, translation ◮ Same shape, size, chirality, orientation ◮ can get via translation ◮ Same shape, size, chirality, orientation, position ◮ equality Art Duval Equivalence relations in mathematics, K-16+

  24. Definitions and motivation Fractions Examples Geometry More theory Real life Finer partitions Art Duval Equivalence relations in mathematics, K-16+

  25. Definitions and motivation Fractions Examples Geometry More theory Real life Finer partitions ◮ As we go down that ladder, we refine the partition, by splitting each part into more parts. Art Duval Equivalence relations in mathematics, K-16+

  26. Definitions and motivation Fractions Examples Geometry More theory Real life Finer partitions ◮ As we go down that ladder, we refine the partition, by splitting each part into more parts. ◮ Different situations call for different interpretations of when two shapes are “the same”. Art Duval Equivalence relations in mathematics, K-16+

  27. Definitions and motivation Fractions Examples Geometry More theory Real life Money ◮ At the store, 1 dollar equals 4 quarters equals 10 dimes. Art Duval Equivalence relations in mathematics, K-16+

  28. Definitions and motivation Fractions Examples Geometry More theory Real life Money ◮ At the store, 1 dollar equals 4 quarters equals 10 dimes. ◮ At old vending machines, dollar bad, coins good. Art Duval Equivalence relations in mathematics, K-16+

Recommend


More recommend