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Algebra · Iteration

Chapter 1 · 3

The idea

Rearranging an equation into iterative form

How "show that the equation can be written as x = g(x)" works — isolate a lone x by honest rearranging — and why that form is exactly what an iteration machine needs.

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Algebra · Iteration

Rearranging an equation into iterative form

How "show that the equation can be written as x = g(x)" works — isolate a lone x by honest rearranging — and why that form is exactly what an iteration machine needs.

Why it works

Feeding a machine that eats x

The change-of-sign lesson trapped a root of x3−3x−5=0x^3 - 3x - 5 = 0 between 22 and 33 — but trapping is not finding. The finder is an iteration machine: feed in a guess, and a better guess comes out. The catch is the machine's inlet shape. It only accepts equations written as

x=g(x)x = g(x)

— "xx equals a formula involving xx" — because that is what lets an estimate be fed in on the right to produce a new estimate on the left. So exam questions say: *"show that the equation can be rearranged to give x=3x+53x = \sqrt[3]{3x + 5}."* That step is the adapter, and it is pure rearranging.

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