c) First, we need to convert 7π/6 radians to degrees. π radians are equivalent to 180°, then:

From the table:

8π/3 can be expressed as follows:

The function tan(x) is periodic, with a period of π. This means that evaluating:

is the same as evaluating:

In this case, x (the input in the function) is translated 2π units to the left. From the periodicity of the function, the values are the same.
2π/3 radians is converted to degrees as follows:

From the table:
![\tan ((2)/(3)\pi)=\tan (120^o)=-\sqrt[]{3}](https://img.qammunity.org/2023/formulas/mathematics/college/989f5eh0n8104sxu1npfr7olsug3nfhj4a.png)
Substituting these values into the original expression:
![\begin{gathered} \sin ((7\pi)/(6))\cdot\tan ((8)/(3)\pi)= \\ =\sin ((7\pi)/(6))\cdot\tan ((2)/(3)\pi)= \\ =(-(1)/(2))\cdot(-\sqrt[]{3})= \\ =\frac{\sqrt[]{3}}{2} \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/1hn1crbdifo2rc9wtbtsfonio4zbh8nn80.png)