12. Let C be a variable path in the ay-plane of arc-length 1 starting at the point (632951765115a.jpg,1) and ending at the point (a,b). Suppose that G(a,b) := 63295197d9d18.jpg .dr, where f(x,y) := arctan 632951b5f362c.jpg, 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)__.