Find the reference angle of - 9pi/7

5pi/7.

Step-by-step explanation:

That would be 2 pi - 9pi/7

= 5pi/7.

2π/7

Step-by-step explanation:

The reference angle is the smallest angle between the terminal ray and the x-axis. It is always a positive value. Here, the terminal ray is in the 2nd quadrant, 2π/7 radians clockwise from the - x axis.

It makes an angle of 2π/7 radians with the - x axis, and an angle of 5π/7 radians with the + x axis. The reference angle is the smallest of these, so is 2π/7 radians.

The reference angle of - 9π/7 is 2π/7 radians.