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Problem 17 - Entrance Test

The expression (x² + 1/x²)² - 4 equals

Correct: B

(x² + 1/x²)² - 4 = x⁴ + 2 + 1/x⁴ - 4 = x⁴ - 2 + 1/x⁴ = (x² - 1/x²)².