English

Prove that the Function F ( X ) = { X | X | + 2 X 2 , X ≠ 0 K , X = 0 Remains Discontinuous at X = 0, Regardless the Choice of K. - Mathematics

Advertisements
Advertisements

Question

Prove that the function 

\[f\left( x \right) = \begin{cases}\frac{x}{\left| x \right| + 2 x^2}, & x \neq 0 \\ k , & x = 0\end{cases}\]  remains discontinuous at x = 0, regardless the choice of k.
Advertisements

Solution

The given function can be rewritten as: 

\[f\left( x \right) = \begin{cases}\frac{x}{x + 2 x^2}, x > 0 \\ \frac{- x}{x - 2 x^2}, x < 0 \\ k, x = 0\end{cases}\]
\[\Rightarrow f\left( x \right) = \begin{cases}\frac{1}{2x + 1}, x > 0 \\ \frac{1}{2x - 1}, x < 0 \\ k, x = 0\end{cases}\]

We observe

(LHL at x = 0) =

\[\Rightarrow f\left( x \right) = \begin{cases}\frac{1}{2x + 1}, x > 0 \\ \frac{1}{2x - 1}, x < 0 \\ k, x = 0\end{cases}\]
\[\lim_{h \to 0} \frac{1}{- 2h - 1} = - 1\]

(RHL at x = 0) =

\[\lim_{h \to 0} \frac{1}{- 2h - 1} = - 1\]
\[\lim_{h \to 0} \frac{1}{2h + 1} = 1\]

So, ​

\[\lim_{h \to 0} \frac{1}{2h + 1} = 1\]

\[\lim_{x \to 0^-} f\left( x \right) \text{and} \lim_{x \to 0^+} f\left( x \right)\]

Thus, f(x) is discontinuous at x = 0, regardless of the choice of k.

 
shaalaa.com
  Is there an error in this question or solution?
Chapter 9: Continuity - Exercise 9.1 [Page 19]

APPEARS IN

RD Sharma Mathematics [English] Class 12
Chapter 9 Continuity
Exercise 9.1 | Q 24 | Page 19

RELATED QUESTIONS

Discuss the continuity of the following functions. If the function have a removable discontinuity, redefine the function so as to remove the discontinuity

`f(x)=(4^x-e^x)/(6^x-1)`  for x ≠ 0

         `=log(2/3) ` for x=0


Prove that the function f(x) = xn is continuous at x = n, where n is a positive integer.


Find all points of discontinuity of f, where f is defined by:

f(x) = `{(2x + 3", if"  x<=2),(2x - 3", if"  x > 2):}`


Find all points of discontinuity of f, where f is defined by:

f(x) = `{(|x|+3", if"  x<= -3),(-2x", if" -3 < x < 3),(6x + 2", if"  x >= 3):}`


Find all points of discontinuity of f, where f is defined by:

f(x) = `{(|x|/x", if"  x != 0),(0", if"  x = 0):}`


Find all points of discontinuity of f, where f is defined by:

f(x) = `{(x/|x|", if"  x<0),(-1", if"  x >= 0):}`


Find all points of discontinuity of f, where f is defined by:

f(x) = `{(x+1", if"  x>=1),(x^2+1", if"  x < 1):}`


Find all points of discontinuity of f, where f is defined by:

f(x) = `{(x^3 - 3", if"  x <= 2),(x^2 + 1", if"  x > 2):}`


Is the function defined by f(x) = `{(x+5", if"  x <= 1),(x -5", if"  x > 1):}` a continuous function?


Using mathematical induction prove that  `d/(dx) (x^n) = nx^(n -1)` for all positive integers n.


Show that the function f(x) = `{(x^2, x<=1),(1/2, x>1):}` is continuous at x = 1 but not differentiable.


Test the continuity of the function on f(x) at the origin: 

\[f\left( x \right) = \begin{cases}\frac{x}{\left| x \right|}, & x \neq 0 \\ 1 , & x = 0\end{cases}\] 


For what value of λ is the function 
\[f\left( x \right) = \begin{cases}\lambda( x^2 - 2x), & \text{ if }  x \leq 0 \\ 4x + 1 , & \text{  if } x > 0\end{cases}\]continuous at x = 0? What about continuity at x = ± 1?


Find the points of discontinuity, if any, of the following functions: 

\[f\left( x \right) = \begin{cases}\left| x \right| + 3 , & \text{ if } x \leq - 3 \\ - 2x , & \text { if }  - 3 < x < 3 \\ 6x + 2 , & \text{ if }  x > 3\end{cases}\]

Discuss the Continuity of the F(X) at the Indicated Points : F(X) = | X − 1 | + | X + 1 | at X = −1, 1.


Find the point of discontinuity, if any, of the following function: \[f\left( x \right) = \begin{cases}\sin x - \cos x , & \text{ if }  x \neq 0 \\ - 1 , & \text{ if }  x = 0\end{cases}\]


Prove that `1/2 "cos"^(-1) ((1-"x")/(1+"x")) = "tan"^-1 sqrt"x"`


Show that the function f given by:

`f(x)={((e^(1/x)-1)/(e^(1/x)+1),"if",x,!=,0),(-1,"if",x,=,0):}"`

is discontinuous at x = 0.


If f(x) = `{{:("a"x + 1,  "if"  x ≥ 1),(x + 2,  "if"  x < 1):}` is continuous, then a should be equal to ______.


Find all points of discontinuity of the function f(t) = `1/("t"^2 + "t" - 2)`, where t = `1/(x - 1)`


The number of discontinuous functions y(x) on [-2, 2] satisfying x2 + y2 = 4 is ____________.


`lim_("x"-> 0) sqrt(1/2 (1 - "cos"  2"x"))/"x"` is equal to


The domain of the function f(x) = `""^(24 - x)C_(3x - 1) + ""^(40 - 6x)C_(8x - 10)` is


The function f defined by `f(x) = {{:(x, "if"  x ≤ 1),(5, "if"  x > 1):}` discontinuous at x equal to


Let a, b ∈ R, b ≠ 0. Define a function

F(x) = `{{:(asin  π/2(x - 1)",", "for"  x ≤ 0),((tan2x - sin2x)/(bx^3)",", "for" x > 0):}`

If f is continuous at x = 0, then 10 – ab is equal to ______.


If function f(x) = `{{:((asinx + btanx - 3x)/x^3,",", x ≠ 0),(0,",", x = 0):}` is continuous at x = 0 then (a2 + b2) is equal to ______.


If f(x) = `{{:(cos ((π(sqrt(1 + x) - 1))/x)/x,",", x ≠ 0),(π/k,",", x = 0):}`

is continuous at x = 0, then k2 is equal to ______.


If f(x) = `{{:((log_(sin|x|) cos^2x)/(log_(sin|3x|) cos  x/2), |x| < π/3; x ≠ 0),(k, x = 0):}`, then value of k for which f(x) is continuous at x = 0 is ______.


Let α ∈ R be such that the function

f(x) = `{{:((cos^-1(1 - {x}^2)sin^-1(1 - {x}))/({x} - {x}^3)",", x ≠ 0),(α",", x = 0):}`

is continuous at x = 0, where {x} = x – [x], [x] is the greatest integer less than or equal to x.


Find the value(s) of 'λ' if the function

f(x) = `{{:((sin^2 λx)/x^2",", if x ≠ 0  "is continuous at"  x = 0.),(1",", if x = 0):}`


Find the value of k for which the function f given as

f(x) =`{{:((1 - cosx)/(2x^2)",", if x ≠ 0),(       k",", if x = 0 ):}` 

is continuous at x = 0.


The graph of the function f is shown below.

Of the following options, at what values of x is the function f NOT differentiable?


Share
Notifications

Englishहिंदीमराठी


      Forgot password?
Use app×