AMC 10A 2007 Problem 20

Past Contests AMC 10 AMC 10A - 2007
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1

Suppose that the number a satisfies the equation 4=a+a^{-1}. What is the value of a^{4}+a^{-4} ?

Answer Choices
A. 164
B. 172
C. 192
D. 194
E. 212