# Please help!!! 2 vector problems! (Cross product)

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• Apr 21st 2008, 05:06 AM
cyy
Please help!!! 2 vector problems! (Cross product)
Let a = [ 1, 1, 0 ], b = [-1, 2, 0 ], c = [ 2, 3, 1 ], d = [ 5, -7, 2 ]

Q1. b x ( b x c )
Q2. ( a - b ) x ( a - c ) + d

May I know how should I solved above?

Best regards
cyy
• Apr 21st 2008, 05:19 AM
mr fantastic
Quote:

Originally Posted by cyy
Let a = [ 1, 1, 0 ], b = [-1, 2, 0 ], c = [ 2, 3, 1 ], d = [ 5, -7, 2 ]

Q1. b x ( b x c )
Q2. ( a - b ) x ( a - c ) + d

May I know how should I solved above?

Best regards
cyy

Q1 Many approaches. You can calculate a = b x c and then calculate b x a. Or you can use the formula for the vector triple product: Vector Triple Product -- from Wolfram MathWorld (then you only have to calculate scalar products).

Q2 Get e = a - b and f = a - c. Now calculate e x f. Add d to the result.

You should know how to calculate a cross/vector product ....

Slightly off-topic but this thread is too good an opportunity to pass up:

Question: What do you get when you cross a mountain-climber with a mosquito?
Answer: Nothing - You can't cross a scaler with a vector.
• Apr 21st 2008, 05:50 AM
cyy
Thx for your help!!! very appreciate for ur effort!
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