Hi. Every time i read physics I feel so discouraged by my lack of understanding in terms of vector calculus and trigonometry. I do understand basic trigonometry and basic vectors but when professors or textbooks move onto combining derivatives with vectors i lack understanding of wich rules apply to vectors when combined with calculus, and also how to interprete it. I really need some good book recomendations for brushing up on this and understanding it clearly and intuitively. And example would be the motion of a particle where r(t) is a vector and i,j are unit vectors. r(t) = r(i*coswt + j*sinwt) The professor says "we can see from this that the length of the vector is one" But for me this does not make sense, how can we see this, and how do we apply the length formyla |r|=sqrt(a^2 + b^2) on the r(t) equation? Please help me with some good physics/calculus math books, that are easy and clear to understand and explain the subjects in detail. I did try Calculus: An Intuitive and Physical Approach by Morris, but i don't find that it explains trigonometry very well and had to quit after the first 100 pages.