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IMAS 2016 — Junior — Round 1 Question 17

IMAS · IMAS 2016 — Junior — Round 1

Question 17

The number $a$ is 5 more than its reciprocal. What is the value of $(a^2-1)^2-125a$?
  1. $5$
  2. $25$
  3. $125$
  4. $\frac{1+\sqrt{21}}2$
  5. $5\sqrt{21}$