Let fbe the function dened as follows. y:f(x):7x28x+1 (a) Find the differential of f. dy: (b) Use your result from part (a) to find the approximate change in y ifx changes from 2 to 1.81. (Round your answer to four decimal places, if necessary.) (c) Find the actual change in y ifX changes from 2 to 1.81 and compare your result with that obtained in part (b). (Round your answer to four decimal places, if necessary.) (d) Compare your result in part (c) with that obtained in part (b) by calculating the absolute value of their difference. (Round your answer to four decimal places, if necessary.) Idrsy|=|:| Find the relative maxima and relative minima, if any, of the function. (Enter your answers as a comma-separated list. If an answer does not exist, enter DNE.) x)=3x476x3+3 Relative maximum value( s): Relative minimum value(s): Determine where the function is concave upward and where it is concave downward. (Enter your answer using interval notation. If an answer does not exist, enter DNE.) x)=3x418x3+x9 Concave upward: Concave downward