Question

the measure of angle O is 7pi/6. The measure of its reference angle is.... ° and sin O is .....

Answer 1

$\frac{7 \pi }{6}$ is in the 3rd quadrant... (It is also 210 degrees)
To find the reference angle (which is the distance to the x-axis)
$\frac{7 \pi }{6} - \pi = \frac{ \pi }{6}$  (or 30 degrees)

sin $\frac{ \pi }{6} = \frac{1}{2}$