for f(x) = 0, we have the equation x^4 -8x^2 +11 = 0
we can notice that x^4 is the same as (x^2)^2 by power laws
so we actually have a hidden quadratic in this equation of degree 4, and if we replace x^2 with 'u' , this means that x^4 = u^2 , and 8x^2 is 8u. we can then use the quadratic formula...