Question

How was usin(pi/6) and ucos(pi/6) taken?

Answer 1

cos θ = adjacent / hypotenuse

sin θ = opposite / hypotenuse

Answer 2

The other answer is perfect. To add to it:

In physics we often have the hypotenuse and want to get the other two legs. If you're going "through" the angle, multiply by cos(θ). If you're going "away" from the angle, multiply by sin(θ).