Question: A bug of Minpoly?

When I use evala(Minpoly(sqrt(3) + sqrt(2), x)), then I get a right answer: x^4 - 10*x^2 + 1

But when I want to get the minimal polynomial of cos((2*Pi)/7) by evala(Minpoly(cos((2*Pi)/7), x)), I will get a result:

x - cos((2*Pi)/7)

It clearly does not follow the definition of a minimal polynomial. Is it a bug of Minpoly or I have missed something?

Please Wait...