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1975 AMC 12 Question 30

AMC12 · 1975 AMC 12

Question 30

Let $x=\cos36^\circ-\cos72^\circ.$ Then $x$ equals
  1. $\frac13$
  2. $\frac12$
  3. $3-\sqrt6$
  4. $2\sqrt3-3$
  5. none of these