. Find fx, fy, and fz for the function f ( x , y , z ) = z ( x' ) ( x > 0 , y > 0, z > 0 ). . Suppose f is a differentiable function whose cross-section for y = 5 is f(x, 5) = 3Vx- x2. Find fx(1, 5). . A company's profit (in dollars) when using x units of capital and y units of labor is given by TT ( x , y) = 4X ty - 80 60 The company currently uses 40 units of capital and 120 units of labor. Use differentials to estimate the company's change in profit if it increases capital to 42 units and decreases labor to 119 units