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Let 
f(x)={[(15 x)/(x^(3)+3x)," for "x!=0],[k," for "x=0]:}

f is continuous for all real numbers.
What is the value of 
k ?
Choose 1 answer:
(A) 5
(B) 0
(C) 8
(D) 3

Let f(x)={15xx3+3xamp; for x0kamp; for x=0 f(x)=\left\{\begin{array}{ll}\frac{15 x}{x^{3}+3 x} & \text { for } x \neq 0 \\ k & \text { for } x=0\end{array}\right. \newlinef f is continuous for all real numbers.\newlineWhat is the value of k k ?\newlineChoose 11 answer:\newline(A) 55\newline(B) 00\newline(C) 88\newline(D) 33

Full solution

Q. Let f(x)={15xx3+3x for x0k for x=0 f(x)=\left\{\begin{array}{ll}\frac{15 x}{x^{3}+3 x} & \text { for } x \neq 0 \\ k & \text { for } x=0\end{array}\right. \newlinef f is continuous for all real numbers.\newlineWhat is the value of k k ?\newlineChoose 11 answer:\newline(A) 55\newline(B) 00\newline(C) 88\newline(D) 33
  1. Define Limit of f(x)f(x): To determine the value of kk that makes f(x)f(x) continuous at x=0x = 0, we need to find the limit of f(x)f(x) as xx approaches 00 from both the left and the right. If the limit exists and is equal to kk, then f(x)f(x) is continuous at x=0x = 0.
  2. Factor Out x: We calculate the limit of the function as x approaches 00:\newlinelimx015xx3+3x\lim_{x \to 0} \frac{15x}{x^3 + 3x}\newlineWe can factor out an x from the denominator:\newlinelimx015xx(x2+3)\lim_{x \to 0} \frac{15x}{x(x^2 + 3)}\newlineNow we can simplify the fraction by canceling out the common x term:\newlinelimx015x2+3\lim_{x \to 0} \frac{15}{x^2 + 3}
  3. Evaluate Limit at x=00: As x approaches 00, the x^22 term also approaches 00, so we can evaluate the limit by substituting x with 00:\newlinelimx0150+3=153=5\lim_{x \to 0} \frac{15}{0 + 3} = \frac{15}{3} = 5
  4. Determine Value of kk: Since the limit of f(x)f(x) as xx approaches 00 is 55, for ff to be continuous at x=0x = 0, kk must be equal to 55. This is because the definition of continuity at a point requires that the limit of the function as it approaches the point from both sides is equal to the function's value at that point.

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