X4 - 17x2 + 16 = 0 Rewrite the equation in terms of u

You probably are interested in expressing the given equation as a quadratic equation in u, as it will make it easy to find the solutions.

Let u = x²

So,

u² = x⁴

So, the given equation can be written as:

u² - 17u + 16 = 0

Now the equation is quadratic in u and the solutions can be calculated using quadratic formula or factorization.