This booklet contains short articles, most of which have been printed in the LMFK member

magazine for Danish upper secondary school math teachers. Thus, (2013.6) indicates that the article has been published in magazine nr. 6 from 2013. The goal is to show how mathematics formulas may be discovered by working with ordinary playing cards. Some formulas are limited by the fact that cards only have positive numbers, so the question if the formulas also apply to negative numbers may be partly answered by testing.

The article on Heron’s formula is the only one not using playing cards.

Content

01. The little, medium and big Pythagoras with 3, 4 and 5 playing cards (2015, 2) …………1

02. PI with three playing cards (2014, 6) ………………………………………………………………….3

03. Proportionality with the 2 playing cards (2015, 1) ………………………………………………..4

04. Product rules with 2-4 playing cards (2014, 6) …………………………………………………….5

05. The quadratic equation with 2 playing cards (2014, 4) ………………………………………….6

06. Change by adding and multiplying with playing cards …………………………………………..7

07. The saving formula with 9 playing cards (2014, 2) ……………………………………………….8

08. The change of a product with 3 playing cards (2013, 6) ………………………………………..9

09. Integral- and differential calculus with 2 playing cards (2015, 1) ………………………….. 10

10. Differentiating sine and cosine with 3 playing cards (2014, 4) ……………………………… 11

11. Topology with 6 playing cards ………………………………………………………………………… 12

12. Heron’s formula, triangle circles and Pythagoras in factor form (2011, 6) ………………13