To determine which points might be in the table of values for the function \( g(x) = \cos(-1.5x) - 1 \), we first need to evaluate \( g \) at the specified inputs.
Step 1: Calculate \( g(x) \) for \( x = \frac{2\pi}{3} \)
\[ g\left(\frac{2\pi}{3}\right) = \cos\left(-1.5 \times \frac{2\pi}{3}\right) - 1 \]
Calculating \( -1.5 \times \frac{2\pi}{3} \):
\[ -1.5 \times \frac{2\pi}{3} = -\pi \]
Now, we find \( \cos(-\pi) \):
\[ \cos(-\pi) = -1 \]
Therefore,
\[ g\left(\frac{2\pi}{3}\right) = -1 - 1 = -2 \]
This means the point \( \left(\frac{2\pi}{3}, -2\right) \) is valid.
Step 2: Check the other options.
For \( x = \frac{2\pi}{4} = \frac{\pi}{2} \):
\[ g\left(\frac{\pi}{2}\right) = \cos\left(-1.5 \times \frac{\pi}{2}\right) - 1 \]
Calculating \( -1.5 \times \frac{\pi}{2} \):
\[ -1.5 \times \frac{\pi}{2} = -\frac{3\pi}{4} \]
Now, we find \( \cos\left(-\frac{3\pi}{4}\right) \):
\[ \cos\left(-\frac{3\pi}{4}\right) = -\frac{\sqrt{2}}{2} \]
Therefore,
\[ g\left(\frac{\pi}{2}\right) = -\frac{\sqrt{2}}{2} - 1 \]
This value is not zero. Thus \( \left(\frac{2\pi}{4}, 0\right) \) is not valid.
Summary of results:
- The point \( \left(\frac{2\pi}{3}, -2\right) \) is valid.
- The value \( g\left(\frac{2\pi}{3}\right) = -2 \).
- The point \( \left(\frac{2\pi}{4}, 0\right) \) is invalid.
Therefore, the answer to the question "which of the following could be found in a table of values" is:
a. \( \left(\frac{2\pi}{3}, -2\right) \).