Circle by Radius - Cinderella Documentation
Description: The user's guide to the Interactive Geometry Software Cinderella

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# Circle by Radius

This mode allows a circle defined by its center and its radius to be added. When the center of such a circle is moved, the radius remains constant. However, in move mode it is also possible to select the boundary of the circle itself and change the radius.

This mode generates the circle together with its center with just one press–drag–release sequence. When the mouse is pressed, the center is added. Dragging the mouse generates the circle. Its boundary remains attached to the mouse pointer. When the mouse is released, the position of the circle is frozen, and the construction is finished. The logic behind this mode is analogous to that in Line through a Point mode.

Constructing a circle in this mode can be described as a three-step procedure:

- Pressing the left mouse button generates the center. The definition of this point depends on the position of the mouse at the moment the button is pressed, as in add a line mode.
- Dragging the mouse generates the circle. The radius can be adjusted freely. The circle also snaps to existing points if they are selected at the current mouse position.
- Releasing the mouse button freezes the definition of the circle. The construction is then finished. Depending on the final position of the mouse pointer two things can happen:
- Either a circle by radius is added,
- or, if the mouse pointer is over an existing point, then this point is used as a circumference point for the circle. The circle is bound to that point.

#### Synopsis

Circle by radius mode creates a circle with freely chosen radius with a press–drag–release sequence.

#### Caution

The actual "shape" of a circle depends on the choice of the geometry.

#### See Also

- Add a Circle
- Circle by Fixed Radius
- Line through a Point