The center of the circle (of both circles) is at the point (4,0). Find the distance from the point (4,0) to the straight line 4x + 5y = 7. For it, use the formula for the distance from the point to the straight line in a coordinate plane (for example, from the lesson The distance from a point to a straight line in a coordinate plane in this site). d == . (Do not miss "d" with the diameter! In opposite, the "d" is the radius: r = , and = . ) Now the equation of the circle is = .
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