(1) is to expand and simplify this function expression and get 2sin(pi/4-x). Then periodically, pi/4-x=2pi+2kpi can be used to find the minimum value, and pi/4-x=kpi can be used.

(2) Expand the two formulas given in the question, and then simplify and add them to get 2cos(b)cos(a)=0. B=pi/2 can be obtained according to the size relation, and the result can be obtained by bringing it into the expression of f(x).