Asked by maath
Find a vector of length 3 that is perpendicular to [2,1,-2]
Answers
Answered by
Reiny
First we need a perpendicular, any one will do as long as the dot product is zero. How about
(2,1,-2)dot(1,4 a) = 0
2 + 4 - 2a = 0
-2a = -6
a = 3
so (1,4,3) is a normal
now we have to stretch to a length of 3
length of my choice = (1/√26)
so a unit vector is (1/√26)[1,4,3)
and one of length 3 is
(3/√26([1,4,3]
of course this answer is not unique, there would be an infinite number of answers.
(2,1,-2)dot(1,4 a) = 0
2 + 4 - 2a = 0
-2a = -6
a = 3
so (1,4,3) is a normal
now we have to stretch to a length of 3
length of my choice = (1/√26)
so a unit vector is (1/√26)[1,4,3)
and one of length 3 is
(3/√26([1,4,3]
of course this answer is not unique, there would be an infinite number of answers.
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