First, if 3 is less than π, we can probably guess that it is the second quadrant angle, so we take+;

Second, π/2

Third, 6 is more troublesome. Think about it. 2π is 2*3. 14=6. 18, so it is a little smaller than 2π, and 2π is the fourth quadrant, so the cosine of the fourth quadrant should be+.

Solution 2: If you know 1 radian = 57.30, you can change it to angle calculation.