Solve Total Differential: Find \Deltaz for z(x,y)

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SUMMARY

The discussion focuses on solving the total differential for the function z(x,y) = (x^2)y - 3y. The user successfully calculated the partial derivatives, obtaining ∂z/∂x = 2xy and ∂z/∂y = x^2 - 3. They determined dz to be 0.02 but expressed uncertainty regarding the calculation of Δz, which represents the true difference in function values at the specified points. The correct approach to find Δz involves evaluating z(3.99, 3.02) - z(4, 3).

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  • Understanding of partial derivatives in multivariable calculus
  • Familiarity with the concept of total differential
  • Basic knowledge of evaluating functions of two variables
  • Proficiency in calculating limits and differences in calculus
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  • Learn how to compute total differentials in multivariable functions
  • Study the application of Taylor series for approximating function values
  • Explore numerical methods for evaluating function differences
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Students studying multivariable calculus, educators teaching calculus concepts, and anyone looking to deepen their understanding of total differentials and their applications.

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Homework Statement



For:
z(x,y)=(x^2)y-3y
Find \Deltaz and dz when x=4, y=3, \Deltax=-0.01, \Deltay=0.02

Homework Equations





The Attempt at a Solution



I got the partial derivatives:

df/dx=2xy, and df/dy=x^2-3

and solved dz=0.02

However, I don't know how to find \Deltaz
 
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Delta z is the true difference. z(3.99,3.02)-z(4,3).
 
Question: A clock's minute hand has length 4 and its hour hand has length 3. What is the distance between the tips at the moment when it is increasing most rapidly?(Putnam Exam Question) Answer: Making assumption that both the hands moves at constant angular velocities, the answer is ## \sqrt{7} .## But don't you think this assumption is somewhat doubtful and wrong?

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