hi, could someone help me with this please:

a polynomial is given by $\displaystyle p(x) = x^3 - 6x^2 + 9x - 4$

a) factorise p(x) completely- i did this question and came up with $\displaystyle (x - 1)^2 (x - 4)$ but then the next question i didn't get

b) hence solve the equation $\displaystyle y^6 - 6y^4 + 9y^2 - 4 = 0$

i'm guessing its something to do with the second equation being the same as the first one but with x squared, so $\displaystyle y = x^2$. but the answer in the book is $\displaystyle y = \pm 1$ and $\displaystyle y = \pm2$ could someone please explain this? thankyou, mark