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2007 AMC 10A Question 20

AMC10 · 2007 AMC 10A

Question 20

Suppose that the number $a$ satisfies the equation $4 = a + a^{-1}.$ What is the value of $a^4 + a^{-4}?$
  1. $164$
  2. $172$
  3. $192$
  4. $194$
  5. $212$