H2 Vectors (Math)

• SBS1985C

  16 Mar 10, 23:17

  Hi! Hope anybody could help me check my answer for this question. I think my lecturer provided the wrong ans / typo in qn. Ans Given: 1/SqROOT17
  
  
  l_1 : r = ( -1,3,-3) + X (2,-1,2)  l_2 : r = ( -3,1,-2) + Y (2,3,2)

   

  Find angle between l_1 and l_2

   

  My Working.
  a.b = |a| |b| CosZ
  (2,-1,2).(2,3,2) = SqROOT153 Cos Z
  Cos Z = 3/SqROOT153= 1/SqROOT17 <- Could the qn been asking Find the Cosine of the angle between L_1 and L_2?
  
  Z = 1.32 =/= 1/SqROOT17
  
  Thanks in advance to anyone to reads or reply to this msg =)

• wee_ws

  17 Mar 10, 07:39

  Hi,

    Angle between two lines is equivalent to angle between their direction vectors.

    So cos theta = 5 / [3 sqrt(17) ].

    Typo errors are common, so be sure to check with classmates.

    Thanks.

  Cheers,
  Wen Shih