Monday 14 March 2016

calculus - Determine the value of $k$, if any, that makes k continuous everywhere for this piece wise function.




Let
$$

h(x) =
\begin{cases}
\sin (kx), & \text{if }x\leq 2, \\
x+k^2, & \text{if }x>2,
\end{cases}
$$
where $k$ is a real constant. Determine the value of $k$, if any, that makes k continuous everywhere.




I done my work and here goes.






Since $h(x)$ is continuous on $(-\infty,2)$ and on $(2,\infty)$, it suffice to find the value of $k$ such that $h(x)$ is continuous at $x=2$.



Suppose $h(x)$ is continuous at $x=0$, then $$\lim_{x\to2^-}h(x)=\lim_{x\to2^-}\sin k(x)=\sin(2k)$$
and $$\lim_{x\to2^+}h(x)=\lim_{x\to2^+}x+k^2=2+k^2$$
Therefore, $\lim_{x\to2^+}h(x)=\lim_{x\to2^-}h(x)$ implies $\sin(2k)=2+k^2$






Ok so now I am stuck. Thanks in advance for helping me out!


Answer



Your work so far is fine.



Hint: $\sin(-)$ is always between -1 and 1.


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