Exercise 1: Limit of a Sequence and the Golden Ratio (Minus 1)

in DTubeyesterday


In this video I show that the limit of a sequence is the same if the sequence was shifted by 1 term. I use this fact to solve for the limit of a recursive sequence by plugging in the limit into the recursion relation itself. Using the definition of a limit, shifting n to n + 1 doesn't fundamentally change the limit, thus the limits are the same. The recursive sequence I look at starts at 1 and has a recursion relation 1 / (1 + previous term). Solving this limit yields a quadratic equation, and solving this for the positive limit term yields THE golden ratio but subtracted by one: 0.6180339... Amazing stuff!

#math #sequences #goldenratio #education #calculus

Timestamps:

  • Exercise 1: 0:00
  • Solution to Part (a): 0:30
    • Replacing n with n + 1 in the definition of a limit: 2:02
  • Solution to Part (b): Recursive sequence: 4:30
    • Plugging in the limit into the recursion relation: 6:22
    • Recall the Quadratic equation: 7:14
    • Solving the limit using Quadratic formula: 7:55
    • Limit is positive so take the positive solution: 9:35
    • Solution is the golden ratio phi minus one: https://en.wikipedia.org/wiki/Golden_ratio 9:45

Notes and playlists:


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