## eroshea Group Title An isosceles triangle ABC, in which AB=BC=6 root 2 and AC=12 is folded along the altitude BD so that planes ABD and BDC form a right dihedral angle. Find the angle between side AB and its new position. one year ago one year ago

1. experimentX Group Title

could you draw a bit of figure?

2. eroshea Group Title

i can't .. that is my problem, too..

3. experimentX Group Title

|dw:1353425869624:dw|

4. experimentX Group Title

|dw:1353426012864:dw|

5. eroshea Group Title

so what i'm going to find is the theta??

6. eroshea Group Title

Find the angle between side AB and its new position. what does this mean?

7. experimentX Group Title

i guess that's the angle you are going to find ... can you find it?

8. eroshea Group Title

i need further solution/explanation

9. experimentX Group Title

|dw:1353426445410:dw|

10. eroshea Group Title

that is 90 degrees

11. eroshea Group Title

i used cosine law

12. experimentX Group Title

$$\theta$$ will be half of $$\alpha$$

13. eroshea Group Title

45 ?

14. eroshea Group Title

the book's answer is 60 degrees.. but i find it 45 degrees.. how did it ended up with 60?

15. experimentX Group Title

yep .. should be around like that if you did it properly!!

16. eroshea Group Title

aawww. can you explain it ?

17. experimentX Group Title

looks like you did it right http://www.wolframalpha.com/input/?i=12^2+%3D+2%286+sqrt%282%29%29^2+-+2+*+%286+sqrt%282%29%29^2+cos%28x%29

18. eroshea Group Title

b^2 = a^2 + c^2 - 2ac cos theta that is cosine law right? and the answer is 90 degrees