Integral of a function of various variables

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SUMMARY

The discussion centers on the integral of a function of multiple variables, specifically z = f(x, y). It establishes that the differential form of z is represented as dz = ∂f/∂x dx + ∂f/∂y dy. The relationship between the derivative of z with respect to t and the functions x(t) and y(t) is clarified, emphasizing that the integral of f with respect to t cannot be simplified without additional information about x(t) and y(t).

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  • Familiarity with differential forms
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  • Basic integration techniques
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Students and professionals in mathematics, particularly those studying calculus, as well as educators looking to enhance their understanding of multivariable functions and integrals.

Jhenrique
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When I have a function z = f(x, y), i. e., a function of various variables, the differential form of z is: dz = \frac{\partial f}{\partial x} dx + \frac{\partial f}{\partial y} dy or the derivative of z is: \frac{dz}{dt} = \frac{\partial f}{\partial x} \frac{dx}{dt} + \frac{\partial f}{\partial y} \frac{dy}{dt} So, analogously, if I take the integral of z wrt t, so how come to be the expression for f?
 
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Jhenrique said:
When I have a function z = f(x, y), i. e., a function of various variables, the differential form of z is: dz = \frac{\partial f}{\partial x} dx + \frac{\partial f}{\partial y} dy or the derivative of z is: \frac{dz}{dt} = \frac{\partial f}{\partial x} \frac{dx}{dt} + \frac{\partial f}{\partial y} \frac{dy}{dt} So, analogously, if I take the integral of z wrt t, so how come to be the expression for f?
When you take the derivative of z with respect to t, you are tacitly assuming that both x and y are functions of t alone. That is, that x = x(t) and y = y(t).

With that assumption, ##\int f(x, y) dt = \int f(x(t), y(t)dt##. As far as I know, that can't be simplified without knowing more about x(t) and y(t).
 

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