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)
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