1. The problem statement, all variables and given/known data E(x,y,t)=(2i/sqrt(5)) + (j/sqrt(5)) Eo cos( 2pi(1/lamda)[2x/sqrt(5) - y/sqrt(5)]-[ft] ) 2. Relevant equations I Know k =2pi/lamda for 1D wave I know K vetor=k dot r I know K vector shows the direction of propogation, and must be perpendicular to E and B. 3. The attempt at a solution Got 1/3 points on this part of my exam. Kvector=2pi (1/lamda) [2/sqrt(5) - 1/sqrt(5)] * (2i/sqrt(5)) + (j/sqrt(5)) I know I have to check for normalizaton, and it is normalized. Obviously this is wrong. I'm not sure how to define k for a multi dimensional wave, and my textbook does not show any example problems for 3 dimensional waves., or shows solutions for any multidimensional waves that involve K. Is the answer simply the resultant vector of kx and ky? sqrt( (2/sqrt(5))^2 + (1/sqrt(5))^2)) which just equals sqrt(1)=1. Edit: Referred back to Griffiths electrodynamics, and think I Figured it out. K vector = K * r = (2pi/lamda) ( 2x^ / sqrt(5) - 1y^ / sqrt(5)) where x^ and y^ indicate the unit vectors xhat and yhat, not x to a power of ____.