How do you get the answer after you have an equation?

The reference angle is : π/9

Explain

Now the given angle is

-8 π/ 9

Now we can see that the angle is negative ( given angle) and it is in the third quadrant then find the reference angle we need to add π to it

Reference angle : - 8 π/ 9

9 π -8 π/ 9

Subtract

π/9

31/6= 19/6 19/6 *1/7=19/42