1. The problem statement, all variables and given/known data I am aving a bit of trouble understanding how to show something is a 4 vector. For example K = (v/c, 1/lamdba, 0, 0 ) Show it is a 4-vector. I am not quite sure how to start this. Similarly I have the amplitude of a wave in frame S described as A=cos[2PI(vt-x/lambda)] and need to show that the amplitude of te wave in S' can be written as cos[2PI(v't'-x'/lambda') 2. Relevant equations 3. The attempt at a solution I am not sure how to do the first part My attempt at the second part vt-x/lambda = vct/c - x/lambda =v/c(gamma(ct'+beta x')) -1/lambda *gamma(x'+beta ct') =ct' gamma(v/c-beta/lambda)-x'gamma (1/lambda-beta v/c) using a similar question in my notes but I don't think this is right and I don't know how it helps???