-1 ≤ sin(x - pi/6) ≤ 1; /*2 -2 ≤ 2 sin(x-pi/6) ≤ 2; /+3; -2 +3 ≤ 2 sin(x-pi/6) +3 ≤ 2 +3; 1 ≤ 3 + 2 sin (x - pi/6) ≤ 5; D(f) [ 1; 5]