which equation will use for those? and pls explain in detail, not only write the steps.

9. For f(x, y), find all values of x and y such that fr(x, y) = 0 and fy(x, y) = 0 simultaneously. Ax, y) = 25x3- 5xy+ 25y' 10. Find the total differential for the function w = 423ysinx.6w 11. Differentiate implicitly to nd K given x2 'l'y2 + 22 5yw + 10w2 = . 12. Given f (x , y) = 16 962 "3/2, use the total differential to approximate AZ at (4, 2) towards (2-1, 1-03). Round your answer to two decimal places. (3w 13. Find s using the appropriate Chain Rule for W =y3 9x2y where x = es and y = e', and evaluate the partial derivative at S = 3 and t = 6. If necessary, round your answer to two decimal places