Answer:

Step-by-step explanation:
The angles are vertical since they form from two lines crossing at a point and they share a same vertex.
Vertical angles are equal so



The best answer would be C
Answer:
Step-by-step explanation: letter B is the right answer
Answer:

Step-by-step explanation:
A circle centered at (0,0) with radius r is 
Since your circle has diameter of 12, then its radius is 6. Then 
So a possible answer is: 
If you want to move the location of the center, but keep it on the x-axis, then add or subtract a number to the x, such as this:

The center of this circle would be (-4, 0) which is still on the x-axis.