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1. center at the origin, radius 7 units
a. find the center
b. find the radius
c. find the equation of the circle

2. center (2,–3), radius 4 units
a. find the center
b. find the radius
c. find the equation of the circle

3. center (–3,–4), tangent to x-axis
a. find the center
b. find the radius
c. find the equation of the circle ​