Calculate f,(x,y), f,(x,x), f,(1, -1), and f,,(1, -1) when defined. (If an answer is undefined, enter UNDEFINED.) f(x, y) 750 + 6 - %3D ,(1, -1) = ,(1, -1)= [ af af af af and y (1, -1) Calculate when defined. (If an answer is undefined, enter UNDEFINED.) (1, -1) f(x, y) = 2x - y + x - 4 af ax af y af ax (1, -1) af %3D ay (1, -1) af af af af and ay l(1, -1) Calculate when defined. (If an answer is undefined, enter UNDEFINED.) (, -1) f(x, y) = 12,000 - 70x + 20y +7xy af af %3D ay af ax (1, -1) af ay (1, -1) Calculate f(x.y), f,(x,v), f(1,-1), and f,(1,-1) when defined. (1f an answer is undefined, enter UNDEFINED.) flx, y) = 2xy 1,(1,-1) =| 1(1,-1)= [ af and af af af Calculate when defined. (If an answer is undefined, enter UNDEFINED.) (1, -1) ay (1, -1) f(x, y) = xy2 + xy? + 3xy af af ay af ax (1, -1) af ay (1, -1)