## ajprincess 3 years ago Can someone plzzz help me?

1. ajprincess

2. alexwee123

ugh vectors :/

3. alexwee123

well i fail at almost anything related w/ 3d so can't help u here :(

4. ajprincess

it's k. thanxx anyway.

5. Roya

dear can u attach graph of this ?

6. ajprincess

I dnt hav it. I hav only the question. Am sorry. :(

7. Roya

ok let's try to solve it step by step together .

8. ajprincess

ha k.:)

9. Roya

|dw:1337928984058:dw|

10. ajprincess

I drew this part. Bt where do v place k?

11. Roya

i just think about it .

12. Roya

do the alpha beta has special meaning or they are just coefficient ?

13. ajprincess

they are just coefficients.

14. Roya

ok we suppose that its in the shape like this

15. ajprincess

k.

16. Roya

17. ajprincess

can u plzz show me the next step if u dnt mind.

18. Roya

dear i'm thinking .

19. ajprincess

Ha k.

20. Roya

dear for writing the plane we need a point and a line which cross the plane am i right ?

21. ajprincess

u mean for writing the eqn of the plane? bt v can write it if v knw the position vectors of thr three points isnt it?

22. Roya

yes so u know out and in multiple .

23. Roya

if u multiple out and b and like this for others plane u have the line and u have the point .

24. ajprincess

sorry I didnt get u?

25. Roya

take a look at it : http://en.wikipedia.org/wiki/Cross_product

26. Roya

@Callisto dear i need help here

27. ajprincess

I hav studied cross product. I dnt get where u apply it here. Am so sorry for disturbing u. Can u plzz explain it a bit more.

28. Roya

i'm not sure i ask a friend for help but what i said is this :

29. Roya

in our question we have a b c vectors , for each plane if u cross product both of them u get the line ortoghonal to the plane and u have the point i mean a1 b1 and the other

30. ajprincess

i tried bt nt getting t. can u plzz help me dear?

31. Roya

u know , i'm not sure about the solution .

32. ajprincess

oh k. Am sorry.

33. Roya

i's so sri because i can't help u . but think about my idea . what if we suppose our space with 3 vector a b c instead i j k ? could we find out the answer ?

34. ajprincess

let me try and see.

35. Roya

dear is it a special tetrahedron ? i mean symmetric or ortoghonal ?

36. Roya

if it has any special feature we can use them .

37. ajprincess

It is nt given. :(

38. Roya

i'm not good at english but is it like this ? http://en.wikipedia.org/wiki/File:Tetrahedron_flat.svg

39. ajprincess

no.

40. Roya

i'm so sri .

41. ajprincess

No problem. Bigg thanxxx for trying to help me.

42. timo86m

Here is how to write the planes of the tetrahedron using vecors I think.

43. ajprincess

I wrote the equations of planes as follows. |dw:1337970519951:dw||dw:1337970602748:dw|

44. ajprincess

I wrote it so cos the equation of a plane through three points is |dw:1337970955268:dw| were r is p.v of any point R on the required plane, a,b and c are p.v of the given points A,B, and C.

45. ajprincess

Am I right @timo86m

46. timo86m

seems right use it to prove those things it says.

47. ajprincess

bt that's the place I am stuck.

48. ajprincess

I got the answer for the first part.:0

49. timo86m

for 1 you can just take vector D to D1 Use vector addition and it will equal RHS

50. timo86m

this is a tough one :) lol

51. ajprincess

I did it in this way. Let the position vector of D1 with respect to D be d1. Since D1 lies in the plane AB|dw:1337972129746:dw| and since DD1//DK|dw:1337972217587:dw||dw:1337972258266:dw||dw:1337972326958:dw||dw:1337972383792:dw| Such a lengthy method.

52. ajprincess

@timo86m if u dnt mind can u help me to solve the third and fourth part.

53. timo86m

oh Sorry I dont think i can

54. ajprincess

it's k. I got an answer. If I make an adjustment to that I am getting it right. Bt am nt sure if I am right. Anyways thanxxx a lot for coming to the rescue.

55. timo86m

LOL I did nothing :P It was all you smartypants

56. ajprincess

:)

57. timo86m

you did it all :) really

58. ajprincess

thanxxx for the medal.:)

59. timo86m

I am proud of you :)

60. ajprincess

:)

61. timo86m

Bring on another q :D Make it easier this time please :P