Posted by **yuni** on Saturday, December 24, 2011 at 9:51pm.

the position vectors of the point A,B & C respect to O are a=3i-2j+4k, b=i+3j-4k, c=-2i+5j-3k. Find

a)the angle between a+b and a-b

b)lamdar if vector a is perpendicular to b+lamdar k.

- math -
**drwls**, Sunday, December 25, 2011 at 6:26am
How do you define "lambdar" ?

As for part (a), compute these two vectors:

a + b = 4i +j +0k

a - b = 2i -5j +4k

Their magnitudes are:

|a+b| = sqrt(16 + 1) = sqrt17

|a-b| = sqrt(4 +25 + 16) = sqrt45

(a+b)*(a-b) = 8 -5 = 3

= (sqrt17) x (sqrt45) cos theta

cos theta = 3/sqrt765 = 0.108

theta = 83.8 degrees

In the above, * denotes a dot product and x denotes normal scalar multiplication

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