Consider the following functions: 12 : R2 defined by = (rcos(r), x). : [O, 67] x x R defined by Ax, y, z) = cos(x) + sin(g) sin(z) : (0, 1) x (0, 1] defined by y) = :r2y2 y) = (zr2 y) (a) For each function, determine if it is either single-variable or multi-variable function and if it is either scalar function or vector function. (b) XVhich function is the easiest to plot? Which function is the second easiest to plot? Which function is the hardest to plot? Explain your answers.