Calculate ∂f ∂x , ∂f ∂y , ∂f ∂x (1, −1) , and ∂f ∂y (1, −1) when defined. (If an answer is undefined, enter UNDEFINED.) f(x, y) = e0.9xy

Joel wants to buy a new tablet computer fram a store having a 20% off sale on all tablets. the tablet he wants has an original cost of $190. he also wants to make sure he has enough money to pay the 5% sales tax. part one joel uses the incorect expression 0.95(190)(0.8) to calculate that the tablet will cost him a total of $144.40. describe his error and write the correct expression part two how much will joel pay for the tablet show your work if you answer this question correctly you will receive a prize of 99 points good luck