[填空题]
A function is defined by f;* :m odts9tetx-u5 :o ;8desy5 d0mwy jb5-fbm-n mxf(x)=a cos (k x)+c , for $-\pi \leq x \leq \pi $, where k>0 . Part of the graph of y=f(x) is shown on the diagram below.
1. Find the value of:
1. a ;
2. k ;
3. c .
2. Solve f(x)=2 , for 0$ \leq x \leq \pi$ .
