Homework Help Forum: Vector & Geometry

Posted by Mathwise on Wednesday, November 4, 2009 at 6:33am.

if A= i+j, B= 2i-3j+k and C= 4j-3k find: Ax(BxC) pls help with solution.

• Vector & Geometry - Reiny, Wednesday, November 4, 2009 at 7:44am

  A=[1,1,0] B=[2,-3,1] C=[4,0,-3] Let's do BxC I use a very simple algorith to form the cross-product of two vectors. - write the two vectors above each other 2 -3 1 4 0 -3 - for the first number, with your pinkie or with a pencil, block off the first column and find the right cross-product of the remaining square matrix, that is, (-3)(-3) - (0)(1) = 9 -for the second number, with your pinkie or withe a pencil, block off the middle column and find the negative right cross-product of the remaining matrix, that is -( (2)(-3) - (1)(4) ) = 10 - and finally for the third number, block off the third column and find the right cross-product of the remaining square matrix, that is, (2)(0) - (-3)(4) = 12 So BxC = [9,10,12] ( I always check by taking the dot product of this with the two original vectors, you should get zero) Now repeat by taking [1,1,0]x[9,10,12] I got [12, -12, 1} or 12i - 12j + k

  
  

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