Also, when I have an angle of 90 degrees, why when I punch tan(90) into my calculator it says that I have an error, and then when I punch in cos(90) it gives me zero, is this possible?
Thanks
Definitely possible.
Imagine a right triangle with angle theta at lower left, the right angle at lower right. The side adjacent to theta runs along the bottom of the triangle.
As theta approaches 90 degrees, the adjacent side shrinks, and when theta reaches 90 degrees the adjacent side disappears altogether.
So as theta approaches 90 degrees, the adjacent side approaches 0.
Now,
cos(theta) = adj / hyp, so as theta -> 90 deg, adj -> 0 and cos(theta) -> 0 / hyp = 0.
And
tan(theta) = opp / adj, so as theta -> 90 deg, adj -> 0 and tan-> opp / 0, which is undefined since division by 0 is undefined.