=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