As said in the title, I am having trouble solving this problem:
Find the component form of the vector that represents the velocity of an airplane descending at a speed of 100 mph at an angle of 30 degrees below the horizontal.
This is what I worked out:
The magnitude of the vector is 100
That the direction angle would be 30 degrees
Then, I would put the values into the trigonmetric form of a vector formula to get
$$v=(50\sqrt{3},50)$$
But, when I look at the answer, the book has the answer as
$$v=(-50\sqrt{3},-50)$$
All it has for work is this:
The part that I don't understand is how the book came to the conclusion that the direction angle is 210 degrees. Can someone please explain this to me?