1. The problem statement, all variables and given/known data Let us define 4 vector by 4 co-ordinates:(x1,x2,x3,x4) where (x1,x2,x3) are space components (like x,y,z) and x4 is related to time as x4=ict.Express the following equations in tensor notation. (i)The continuity equation: div J+(del*rho/del t)=0 (ii)The wave equation del2ψ-(1/c2) [del2 ψ/del t2]=0 (iii)What will be the value of j4 instead of above? 2. Relevant equations 3. The attempt at a solution I got totally stuck.Please help me to start with it.