All Junior Cert Technical Graphics posts
• #### Anybody have an easy way to remember the methods of transformation geometry? t34b4g

My summer exams are coming up at the moment and I just find it a little difficult to master.

1. #### 11ND - CCM

I don't know any rhyme or phrase for learning them off but I think because there's only 4 you can do it.

Translation- pick it up and move it

Axial symmetry- a mirror image through a line parallel between P1 and P2.

Central symmetry- bring all points through your central point and step off same distance on the other side.

Rotation- use the triangle rule to rotate the object whatever angle and direction you need to get image (NOTE: clockwise will have pin of compass above your point. Anticlockwise has pin of compass below you point of rotation).

Hope this helps

2. #### nuala[pc

whats the triangle rule for the rotation please?

3. #### 11ND - CCM

I can't really explain it in words. I'll try:

•you have your P1 and P2. You need to find the centre of rotation that turned one point into it's next position.

•triangle rule is applying this to find the centre of rotation. If the instruction says "120* through clockwise", then as I said before you should have the pin of your compass above the line connecting two points.

•so based on the rule o triangles that angles sum to 180, you should draw to 30 degree lines to meet above the line and give the centre of rotation, for counter clockwise the two 30 degree lines should be drawn below the line connecting two points.

•another common angle for rotation is 90 degrees, in this case draw two 45 degree lines: above or below.

•then just connect all points to centre of rotation, and using a protractor create an angle of the desired size.

•rotate the points to hit the other arm of the angle and draw the object in the rotated position.

Hope it helps, not the clearest.

4. #### andreideeu

yes , its called studying

5. #### kiishib

what i learned for the triangle rule was 180-120 =60. 60/2=30. come out 30 degrees from each point and where they meet is where you go 120 degrees from.

6. #### thegreatjoe

the great joe