Vectors help

Hate vectors so much. This is the forst exercise in my book and I can't seem to do it. There aren't any examples on how to do it either:

The vector P has magnitude 10 units and is inclined at 150degrees to the x-axis. Express P as a column vector.

Any help is appreciated as I am lost, thanks.

Draw a triangle with one vertex at the origin, a hypotenuse with length ten and the angle 30 degrees marked in between the negative x-axis and the hypotenuse. Then calculate the height $\sin 30^{\circ} = \frac{y}{10}$ and that's your $\mathbf{j}$ component. The length of the adjacent or base will be your $\mathbf{i}$ component but you will need to tack on a minus sign for obvious reasons.

Ahhhh thanks so much! Got it..
But, how do I know when to use the angle given or 180-given angle?
Because most of these question require you to use the given angle rather than 180-it.

Thanks for your help.

Not a problem, glad that helped - uhm, basically just sketch the triangle and see what angle makes life the easiest. :-)