Using the Construct Menu

Each command on the Construct menu requires you first to select one or more objects in the sketch. These selected objects are called the selection prerequisites of the construction: they are the objects to be used to define the construction itself. (For instance, to use the Midpoint command you must first select one or more segments.) Commands in the Construct menu are enabled only when you’ve selected appropriate prerequisites. If you want to use a command but find that it’s disabled, check the objects you’ve selected in the sketch and compare them with the prerequisites listed in the description of that command.

If a command you wish to use is unavailable, it’s possible you have too few or too many objects selected. Deselect unwanted objects or deselect all objects and try again.