Write a single equation that describes the set of all points (x, y) that are 5 units from the origin or less that 10 units from the point (10, 0).
For starters...
The set of points that are 5 units from the origin would be the circle of radius 5 centred at the origin. What would the equation of the circle be?
The set of points that are less than 10 units from the point (10, 0) would be the region inside (but not including) the circle of radius 10 centred at (10, 0). What would the inequation of that region be?