=cosx-cosxcosπ/3+sinxsinπ/3

= 1/2cosx+sinxsinπ/3

=cosxcosπ/3+sinxsinπ/3

=cos(x-π/3)

That is, from 1≤cos(x-π/3)≤ 1.

That is 1≤f(x)≤ 1.

That is, the minimum and maximum values of the function f(x) in the interval r are-1 and 1 respectively.

2

Multiply f(A)= 1

That is cos (a-π/3) = 1 = cos 0.

That is, A=π/3.

The area of a triangle is s=6, the root number is 3, and b=4.

That is s =1/2bcsina =1/2 * c * 4sin60 = 6 √ 3.

That is c=6.

By a? =b？ +c？ -2bccosA

=4? +(6)? -2*4*6*cos60

=28

That is, a=2√7