Identify the variables and clearly state assumptions made for the following equations: (a) ????1 + ????1 = ????2 + ????2, (b) ????1 + ????1→2 = ????2, (c) ????⃗ =constant, (d) ????⃗⃗???? = ????????????????????????????????, (e) ????⃗1 = ????⃗2