C) (x² - \(\frac{6}{x}\))² + 6\(\left(x² - \frac{6}{x²}\right)\) = - 5 d) \((x² - 5x + 2)(x² - 5x + 1) = 6\)

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c) (x² - \(\frac{6}{x}\))² + 6\(\left(x² - \frac{6}{x²}\right)\) = - 5    
d) \((x² - 5x + 2)(x² - 5x + 1) = 6\)