   refresher math for 3d physics
  Hi,I'm trying to create a physics engine from scratch but i'm having a hard time with my vectors and matrices... I used this stuff in college about 10 years ago... I forget 99% of it :(would anyone have a good link for reference.i.e. Why would I use the dot product of 2 vectors?  (random question)what happens in 3d space if I add 2 matrices?what happens in 3d space if I multiply 2 matrices?etc...   
  mathworld.com and wikipedia.org have really great resources for all maths.Dot productMatrix productMatrix sumThe dot product of two vectors is generally used in 3D graphics to determine if they face toward or away (or parallel) from each other. Line/plane intersection, lighting equations, and many other uses.Matrix multiplication is handy for concatenating multiple transformations matrices of different types into one. ie: Combine seperate rotation and translation matrices into one rotate+translate matrix.Matrix multiplication is anti-commutative, so the multiplication order matters, ie: Concatenating into a rotate+translate is not the same as if you had concatenated it as translate+rotate (the opposite) order.I suppose one could use matrix addition to concatenate like transformation matrices. ie: Two translation matrices into one translation matrix.Also, if you can get your hands on any first-year Linear Algebra textbook, that should be all the reference material you need on-hand to get all the answers you need. :)   ;  thank you   ;  The MIT OpenCourseware page may have some helpful free math classes as well.http://ocw.mit.edu/index.html