1. By considering different paths of approach, show that the function has no limit as (x, y) -------> (0, 0).
f(x, y) = - x / √ x^2 + y^2
2. Find the limit as (x, y) -------> (0, 0) along the path y = x for x > 0.

Respuesta :

Answer:

1. shown below

2. [tex]\frac{-1}{\sqrt{2}}[/tex]

Step-by-step explanation:

We say [tex]\displaystyle \lim_{(x,y)\rightarrow (a,b)}f(x,y)[/tex] exists if the limit remains the same along every path.

Here, f is a function on two variables defined on a disk that contains the point (a,b).

1.

Along y-axis i.e., x = 0:

[tex]\displaystyle \lim_{(x,y)\rightarrow (a,b)}f(x,y)=\displaystyle \lim_{(x,y)\rightarrow (0,0)}\frac{-x}{\sqrt{x^2+y^2}}=\displaystyle \lim_{y\rightarrow 0}\frac{0}{\sqrt{0^2+y^2}}=0[/tex]

Along x-axis i.e., y = 0:

[tex]\displaystyle \lim_{(x,y)\rightarrow (a,b)}f(x,y)=\displaystyle \lim_{(x,y)\rightarrow (0,0)}\frac{-x}{\sqrt{x^2+y^2}}=\displaystyle \lim_{x\rightarrow 0}\frac{-x}{\sqrt{x^2+0^2}}=\displaystyle \lim_{x\rightarrow 0}\frac{-x}{x}=-1[/tex]

As the limit is not the same along different paths, so limit does not exist.

2.

Along the path x = y:

[tex]\displaystyle \lim_{(x,y)\rightarrow (a,b)}f(x,y)=\displaystyle \lim_{(x,y)\rightarrow (0,0)}\frac{-x}{\sqrt{x^2+y^2}}=\displaystyle \lim_{x\rightarrow 0}\frac{-x}{\sqrt{x^2+x^2}}=\displaystyle \lim_{x\rightarrow 0}\frac{-x}{\sqrt{2}x}=\frac{-1}{\sqrt{2}}[/tex]

The value of limit along two different path is not same. Therefore, no limit exist.

The value of limit along y=x is [tex]-\frac{1}{\sqrt{2} }[/tex]

limit of function:

The given function is,

                [tex]f(x,y)=\frac{-x}{\sqrt{x^{2} +y^{2} } }[/tex]

Considering first path is x- axis i.e. y=0

          [tex]\lim_{(x,y) \to (0,0)} f(x,y)= \lim_{(x,y) \to (0,0)} \frac{-x}{\sqrt{x^{2} +0^{2} } }=-1[/tex]

Considering another path is y-axis i.e. x=0

         [tex]\lim_{(x,y) \to (0,0)} f(x,y)= \lim_{(x,y) \to (0,0)} \frac{0}{\sqrt{0^{2} +y^{2} } }=0[/tex]

Since, the value of limit along two different path is not same. Therefore, no limit exist.

Value of limit along path y = x.

   [tex]\lim_{(x,y) \to (0,0)} f(x,y)= \lim_{(x,y) \to (0,0)} \frac{-x}{\sqrt{x^{2} +y^{2} } }=-\frac{1}{\sqrt{2} }[/tex]

Learn more about the limit of function here:

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