Question 692969
u=x^-1


u^2=x^-2


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So


x^-2-6x^-1=-4


becomes


u^2-6u = -4


which turns into 


u^2 - 6u + 4 = 0


Now use the quadratic formula to solve for 'u'. Once you have two solutions for 'u', use them to find the two solutions for 'x'.