Help please! Thanks, answer only if you know how to do this.

2 radians

Step-by-step explanation:

The ratio of the arc length to the circumference is the same as the measure of angle AOB in radians to 2pi. 2pi radians is a full circle. We can now construct an equation, with x being our answer.

First, we try to simplify both sides. Next, we multiply both sides by pi. Then, we multiply both sides by 2. Finally, our answer is 2, so 2 radians.

for the friend request.

when a figure, such as triangle (xyz) is reflected over the line y = x to create x'y'z' the x-coordinates and y-coordinates of the original image (pre-image) will be reversed for the image. (e.g., (x, y) > (y, x)) this means that the pre-image position of the x- and y-coordinates switch places which in turn provides a mirror like image of the original xyz.  

i notice that when i draw a line segment from x to x', that the points are parallel from each other -- they are exactly across from each other and do not intersect with any other points.  

yes, think i would see the same characteristic if you drew the line segment connecting y with the reflecting line and then y' with the reflecting line because of the essence of reflections. because it is a mirror image, each point was effected the same way which leads me to conclude that they same would apply to y and y'.