Using radians as the unit of measurement, we can evaluate the given expression as follows:

sin(-9п) = sin(9п) [since sin(-x) = -sin(x)] = 0 [since sin(nп) = 0 for any integer n]

cos(25п/3) = cos(8п + п/3) [since 25п/3 = 8п + п/3] = cos(п/3) [since cos(x + 2nп) = cos(x) for any integer n] = 1/2

ctg(11п/4) = 1/tan(11п/4) = 1/tan(п/4 + п/2) [since 11п/4 = п/4 + п/2] = -1 [since tan(п/4 + п/2) = -1]

Putting it all together:

sin(-9п) + 2 cos(25п/3) - ctg(11п/4) = 0 + 2(1/2) - (-1) = 3

Therefore, sin(-9п) + 2 cos(25п/3) - ctg(11п/4) = 3.