Answer:f(x)=x8−8x6+19x4−12x3+14x2−8x+9=x8−8x6+16x4+3x4−12x3+12x2+2x2−8x+8+1
which allows us to rewrite f(x) as
f(x)=x4(x2−4)2+3x2(x−2)2+2(x−2)2+1
The first three terms are clearly non-negative, and each reaches their minimum of 0 at x=2 (the first term also has a minimum at x=−2). Thus, the minimum of f(x) must be 1.
This can't really be generalized. (I mean, you can apply the approach generally, but it won't generally give you such a convenient result.) I'm not sure I would have looked for this decomposition of f(x) except for the presence of the question.
Explanation: