Let's double-check the conversion of the cosine function \( f(x) = \cos\left(\frac{1}{3}x - \frac{\pi}{6}\right) \) into a sine function.
We know the identity relating cosine to sine:
\[
\cos(x) = \sin\left(x + \frac{\pi}{2}\right)
\]
To convert our specific cosine function:
- Start by rewriting it as:
\[
\cos\left(\frac{1}{3}x - \frac{\pi}{6}\right) = \cos\left(\frac{1}{3}x - \frac{\pi}{6}\right)
\]
We want to express this in terms of sine. We can also apply the phase shift for cosine:
\[
\cos(\theta) = \sin\left(\theta + \frac{\pi}{2}\right)
\]
However, for our specific case, there's actually a simpler way to express it, using the relationship that can directly relate the negative angle:
\[
\cos\left(\theta\right) = \sin\left(\frac{\pi}{2} - \theta\right)
\]
Substituting in for \( \theta \):
-
We define:
\[
\theta = \frac{1}{3}x - \frac{\pi}{6}
\]
-
Therefore,
\[
f(x) = \cos\left(\theta\right) = \sin\left(\frac{\pi}{2} - \left(\frac{1}{3}x - \frac{\pi}{6}\right)\right)
\]
-
Simplifying this gives:
\[
f(x) = \sin\left(\frac{\pi}{2} - \frac{1}{3}x + \frac{\pi}{6}\right)
\]
-
To combine the constant terms, we convert \( \frac{\pi}{2} \) to a fraction with a common denominator:
\[
\frac{\pi}{2} = \frac{3\pi}{6}
\]
Thus, we can rewrite:
\[
f(x) = \sin\left(\frac{3\pi}{6} - \frac{1}{3}x + \frac{\pi}{6}\right)
\]
This combines to:
\[
f(x) = \sin\left(-\frac{1}{3}x + \frac{4\pi}{6}\right)
\]
Simplifying further:
\[
f(x) = \sin\left(-\frac{1}{3}x + \frac{2\pi}{3}\right)
\]
This means we've correctly converted the function. If we were looking to express \( -\frac{1}{3}x + \frac{2\pi}{3} \) as \(\sin\) with a phase shift, we may not have a direct match with the options.
The original answer \( f(x) = \sin\left(\frac{1}{3} x + \frac{\pi}{3}\right) \) is not quite correct as a direct transformation. The confirmed transformation gives:
\[
f(x) = \sin\left(-\frac{1}{3}x + \frac{2\pi}{3}\right)
\]
This doesn't match the options provided, meaning there may have been a misunderstanding regarding the options listed. If there's a need or preference to interpret it in positive phase shift form, we'd need to manipulate it to check for matching options.
In summary, while the resultant forms may need checking through the given options, the process accurately maps the cosine function to sine with proper total transformations. If the specific form was not given, I apologize for any confusion.