Answer:
see below
Explanation:
These geometries seem to have to do mainly with chords.
In any circle, the perpendicular bisector of a chord passes through the center of the circle.
The relationship between chord length and distance from center can be found using the Pythagorean theorem on the right triangle formed by a radius to the end of the chord, the half-chord length, and the distance from center to chord midpoint. (This is why there are two conflicting answers in problem 3. TU should be given as 7.6, not 7.4.)
Considering the above, it should be no mystery that chords in a circle that are the same length are the same distance from center, and vice versa. When circles have the same radii (as circles C and D in problem 3), the same thing holds.
Any triangle formed by a chord and radii to its ends is (obviously) an isosceles triangle. For chords of the same length, all such triangles are (obviously) congruent.