申論題

12. Let C be a variable path in the ay-plane of arc-length 1 starting at the point (,1) and ending at the point (a,b). Suppose that G(a,b) := .dr, where f(x,y) := arctan , is a function in a and b. Then, G attains its maximum at a =__(14)__ and b =__ (15)__ and the maxinum value of G is __(16)__.