Can a function equal zero if the integral of its product is zero?

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    Function Integral
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Discussion Overview

The discussion revolves around the implications of a function being zero at a specific point and how that affects the value of an integral involving that function. Participants explore whether the integral of a function can be zero if the function itself is zero at a certain point, considering various scenarios and mathematical expressions.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • Some participants propose that if f(x,c)=0, then g(c)=∫abf(x,c)dx should equal zero, suggesting a direct implication from the function being zero to the integral being zero.
  • Others argue that it may be necessary to first calculate g(y) from the integral before substituting c to find g(c), indicating a potential need for a more thorough evaluation.
  • A later reply questions the situation where the integral involves a variable that could cancel out, such as in the case of ∫f(x,t)tdx, raising concerns about the implications of f(x,a)=0 in that context.
  • Another participant clarifies that the conclusion about the integral being zero depends on the nature of the product function and the specific conditions under which f(x,a)=0, emphasizing that not all cases lead to a straightforward conclusion.

Areas of Agreement / Disagreement

Participants express differing views on whether the zero value of a function at a point directly leads to the zero value of an integral, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

Limitations include the dependence on the specific forms of the functions involved and the conditions under which the integrals are evaluated. The discussion does not resolve the mathematical implications of certain expressions or the behavior of functions under integration.

aaaa202
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Suppose you are given a function:

g(y) = ∫abf(x,y)dx
And you are told f(x,c)=0. Does this then imply that:
g(c)=∫abf(x,c)dx=∫0dx = 0
Or are you supposed to calculate g(y) from the integral first and then plug in c to find g(c)?
 
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aaaa202 said:
Suppose you are given a function:

g(y) = ∫abf(x,y)dx
And you are told f(x,c)=0. Does this then imply that:
g(c)=∫abf(x,c)dx=∫0dx = 0
Or are you supposed to calculate g(y) from the integral first and then plug in c to find g(c)?
Your shortcut looks fine to me.
 
But what if the you had something like:
∫f(x,t)tdx
And f(x,a)=0. But the integration would yield something that canceled t?
 
Last edited:
No, not unless the product function with f is sufficiently nasty.
REMEMBER that you are basically adding together the areas of tiny rectangles of height f(x,a)*a in your new case.

If f(x,a)=0 for all those rectangles, then the sum is zero.

IF, however, you had something under the integral sign:
f(x,t)/(t-a), then even though f(x,a)=0, you cannot conclude that f(x,a)/(a-a)=0, or is even defined.
 

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