Pi Formula: The Sword in the Stone
The Basel problem as the sword in the stone; the second version splits the sum into odd and even terms.
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Free for classrooms, worksheets, slides and other non-commercial use under CC BY-NC 4.0, with credit to Ben Orlin.
Cartoon by Ben Orlin, Math with Bad Drawings. https://cartoons.mathwithbaddrawings.com/2016-03-14-pi-formula-the-sword-in-the-stone/ (CC BY-NC 4.0)Transcript
π²/6 = 1 + 1/2² + 1/3² + 1/4² + … splits into The Sword: π²/8 = 1/1² + 1/3² + 1/5² + … and The Stone: π²/24 = 1/2² + 1/4² + 1/6² + …