This is the function.

2(y - 2)4+ (x-1)3 - 9(x -1) ()-2) f (x, y ) = 1+ 20f ( x ly ) = 1+ 2 (y- 2) 2 + ( x - 1 ) 3 - 9 ( x-1 ) (y- 2 ) 20 Of = 2 1 + 2 ( y - 4) 9 + ( x-1)3 - 9(x- 1 ) ( y-2) 2x 2x 20 = 0 + 2 x 0 + 3 ( x - 1 ) 2 x 1- 9 x 1 x (y-2) - 9 x(x-1) x0 20 of = 3 ( x - 1)2 - 9 ( y- 2) dx 20 2 ) of = + 2( y - 4) + (x - 1)3 - 9 ( x-1 ) ( y-2 ) 20 = 0 + 2x 4 x ( y- 4) + 0-9x0 x(y-2) - 9x(X-1) x1 20 of = 8 ( y - 4 ) 3 - 9( x-1 ) dy 20