[填空题]
A function is defined by f(x)=a cos (k x)+c , f vrsst:v4svr)o;cs )4 oo8hme;blcj4* y/slpp sbw57 *r $-\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$ .
