Calculus Chapter on Continuous Functions

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Questions and Answers

What condition must be met for a function f to be continuous at the point (a, b)?

  • For every ϵ > 0, there is δ > 0 such that ∥(x, y) − (a, b)∥ < δ implies |f(x, y) − f(a, b)| < ϵ. (correct)
  • For every δ > 0, there is ϵ > 0 such that ∥(x, y) − (a, b)∥ < ϵ.
  • For every δ > 0, there is ϵ > 0 such that |f(x, y) − f(a, b)| < δ.
  • If f is defined at (a, b), then f is continuous.

Which of the following combinations of continuous functions will also yield a continuous function?

  • All polynomial functions defined on the same domain.
  • The reciprocal of a continuous function if the function is non-zero at the point. (correct)
  • Only the sum of two continuous functions.
  • The product of two continuous functions. (correct)

Under what condition is the composite function g(f(x, y)) continuous at (a, b)?

  • If g is continuous at f(a, b) regardless of f's continuity.
  • If g(f(x, y)) is a polynomial function.
  • If both f is continuous at (a, b) and g is continuous at f(a, b). (correct)
  • If f is continuous at (a, b) and g is not continuous at f(a, b).

Which of the following statements about rational functions is true?

<p>A rational function is continuous at (a, b) if q(a, b) is not zero. (B)</p> Signup and view all the answers

Which of the following functions is continuous?

<p>The function f(x, y) = x^3 sin|y| + cos(x^2 + y). (A), The function f(x, y) = x + y if x, y ∈ ℝ. (D)</p> Signup and view all the answers

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Study Notes

Continuity of Functions

  • A function ( f: D \to R ) is continuous at point ( (a, b) ) in ( D ) if for every ( \epsilon > 0 ), there exists ( \delta > 0 ) such that if ( |(x, y) - (a, b)| < \delta ), then ( |f(x, y) - f(a, b)| < \epsilon ).
  • A function is continuous on D if it is continuous at each point ( (a, b) ) in the domain ( D ).

Algebra of Continuous Functions

  • If ( f ) and ( g ) are continuous at ( (a, b) ), then the following are also continuous:
    • The sum ( f + g )
    • The scalar multiple ( rf ) where ( r \in R )
    • The product ( fg )
    • The quotient ( 1/f ) if ( f(a, b) \neq 0 )

Composition of Continuous Functions

  • For functions ( f: D \to E ) and ( g: E \to R ):
    • If ( f ) is continuous at ( (a, b) ) and ( g ) is continuous at ( f(a, b) ), then the composite function ( g \circ f ) is continuous at ( (a, b) ).

Examples of Continuous Functions

  • Polynomials: Functions like ( p(x, y) = x^2 + y^2 ) and ( p(x, y) = 2x^3y - 3x + y + 1 ) are continuous.
  • Rational Functions: A rational function ( r(x, y) = p(x, y)/q(x, y) ) is continuous at ( (a, b) ) if ( q(a, b) \neq 0 ).
  • Other Functions: Functions such as ( f(x, y) = x^3 \sin |y| + \cos(x^2 + y) ) and ( f(x, y) = e^{x^2 + xy} ) are also continuous.

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