Explanations on how to set it up would be great!
you so so much in
don't reply if you're unsure, i genuinely need ///:

You are standing next to a really big circular lake. you want to measure the diameter of the lake, but you don't want to have to swim across with a measuring tape! you decide to walk around the perimeter of the lake and measure its circumference, and find that it's 400\pi\text{ m}400? m. what is the diameter dd of the lake?

The construction of copying qpr is started below. the next step is to set the width of the compass to the length of ab. how does this step ensure that a new angle will be congruent to the original angle? by using compass take the measures of angle and draw the same arc according to it.

Acircle has a radius of 12.6cm what is the exact length of an arc formed by a central angle measuring 120