# How to use constrain to bisect an angle in this geometry problem?

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In triangle ABC, AD is drawn as angle bisector and BE is drawn perpendicular to AD. I want to draw these two lines and triangle ABC by means of constrains, so that when I move point A (make it bigger or smaller), I can get those two lines move automatically. What kind of constrains should I use? For triangle itself, I use "coincident" constrain. I think this part is correct. Whenever I move a vertex after selecting a line and using red grips, it responds and triangle reshapes. Do we have angle bisector constrain? I draw angle dimension line for two equal angle and tried to impose equal constrain for these two angle but couldn't succeed.

Drawing11.dwg

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The Symmetric should do what you want. Also, I think you can save a few constraints if you make ABC a closed polyline instead of 3 line segments.

http://screencast.com/t/G8zJMJiS

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Dear Nestly

Thanks. Actually what I want is exactly what you have made. The Jing was also very cool and I had seen it before but this time I visited its site and got more info. I will try to download and use it, as it is very productive. Thanks for its introduction.

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I have problem keeping endpoints of lines on the other lines. What sort of constrain should I use for it?

1- I tried to impose coincident constrain to keep point E of BE on AC but it doesn't work

2- Same problem occurs for keeping point D of AD on BC

3- I have no idea on how to keep endpoint A of AD on corner point A of trianle

Deleting one constrain

There is an icon to delete all constrain at once. I want to delete only one constrain. How can I do that. It seams that constrains are not selectable to use "erase"

Edited by khoshravan
delete unnecessary notes
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I have problem keeping endpoints of lines on the other lines. What sort of constrain should I use for it?

Coincident --> Endpoint / Object

1- I tried to impose coincident constrain to keep point E of BE on AC but it doesn't work

When you create a Coincident constraint, look at the command line. Pick the ENDPOINT of BE, and the OBJECT AC

2- Same problem occurs for keeping point D of AD on BC

Same as above

3- I have no idea on how to keep endpoint A of AD on corner point A of triangle

Coincident --> Endpoint / Endpoint

There is an icon to delete all constrain at once.

DELCONSTRAINT

I want to delete only one constrain. How can I do that. It seams that constrains are not selectable to use "erase"

Right click on the constraint icon

Here's another demo http://www.screencast.com/t/fZFTVqzNZ

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Dear Nestly

Thanks so much for your clever and smart solution and presentation using Jing. I really enjoyed it. I think Jing will revolutionize the forums by replying in video clips. It couldn't be better than this. Also I appreciate your time for making this animation.

Autoconstrain: I was unaware of its importance. It is a good tool to use.

Options on constrain: Still I haven't made it a complete habit to have an eye on command line for options. I have missed it for "constrain". I will check it.

One more question on animating dimension lines:

I used the autoconstrain as you suggested and it is perfect. The only missing point is that the angular dimension for BAD (upper left one) is associated with the drawing and its value changes while changing vertexes but the other two (DAC and AGE) are constant and fell apart from the associated objects. (I deleted the BC horizontal constrain)

I am sure there is a solution for this deficiency.

Edited by khoshravan
misstyping
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Whoops, it seems I crossed you up by suggesting you make the ABC triangle into a closed polyline. I still think that's a better solution, but the dimensions are associated with the line segments, so when those lines are turned into a closed polyline, the associativity is (partially) lost. Either leave the ABC triangle as single line segments and constrain the corners, or re-create the dimensions after you create the closed polyline.

Edited by nestly
discovered the error

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