So far in Chapter 10 we have learned about circles in that we know the parts of a circle and we can find the area and circumference. Also in this chapter we have learned about a central angle, arc ( major & minor), inscriced angle, tangent, and a secant. All of these things can help architects and engineers find out there missing angle that they need to design the next building or massive column. that is how circles are used in the real world. A question would be how can circles be so important?