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# Equation of a Circle

- 1Find the radius and the center of the circle that is defined by the equation: $$x^2+y^2=25$$ The general equation for a circle is $$x^2+y^2=r^2$$
- 2Find the radius and the center of the circle that is defined by the equation: $$x^2+y^2=81$$
- 3Find the radius and the center of the circle that is defined by the equation: $$x^2+y^2=40$$
- 4Find the radius and the center of the circle that is defined by the equation: $$(x-3)^2+(y+5)^2=36$$
- 5If the centre of a circle is (0,0) and the radius is 3 cm, find the equation of the circle.
- 6If the centre of a circle is (0,0) and the radius is 7 cm, find the equation of the circle.
- 7Determine the radius of the circle given the centre is at (0,0) and the point (3,4) is a point on the circumference.
- 8Determine the radius of the circle given the centre is at (0,0) and the point (-2,3) is a point on the circumference.

$$e=mc^2$$