Problem 3. Let f(x, y) = 1 +xln(xy − 5). a. Explain why f(x,y ) is differentiable at (2,3). b. Find the linearization L(x,y ) for f(x, y) at (2,3). c. Use part (b) to approximate f(x,y ) at (2.1,2.9) d. Use differential dz to approximate ∆z for z = f(x,y) at (2.1,2.9)