1. The angle between two planes Start To show the dynamic figures properly, the evaluation version of Cabri 3D (V2.0 or above) must be installed.

2. Q1 Q2 Hold down the right mouse button and drag to change the view angle.

3. Q3 Q1 Q2 Hold down the right mouse button and drag to change the view angle.

4. Q4 Q2 Q3 Hold down the right mouse button and drag to change the view angle.

5. Q3 Q4(a) Q4(b) Q4(b) Hold down the right mouse button and drag to change the view angle.

6. Q4(a) Q4(a) Q4(b) Q4(c) Q4(c) Hold down the right mouse button and drag to change the view angle.

7. Q4(b) Q4(b) Q4(c) Hold down the right mouse button and drag to change the view angle.