1. The problem statement, all variables and given/known data [itex]f'_x = kx_k, k = 1, 2, ..., n[/itex] 3. The attempt at a solution The partial should be f(sub)x(sub)k, as in, the partial derivative of [itex]f[/itex] with respect to [itex]x_k[/itex]. I wasn't sure how to represent that using TeX. I'm honestly at a complete loss here, because I'm not entirely sure what the subscripts refer to. I suppose if [itex]k = 1[/itex], then the derivative of [itex]f[/itex] with respect to [itex]x_k[/itex] [itex]= 1x_1[/itex], but that tells me absolutely nothing because I don't even know what that [itex]x_1[/itex] refers to... Any help would be much appreciated!