# P3 Vector qWatch

This discussion is closed.
#1
from heinemann p3 book, p. 188 q 41

r= λi + (2λ-1)j-k
s= (1- λ ) i + 3λ j + (4λ-1)k
(a) find the values of λ for which r & s are perpendicular
when λ=2 r & s are the position vectors of the points A & B respectively.

b. Find AB

c. Use a scalar product to find the size of <BAO
0
14 years ago
#2
(Original post by toxi)
from heinemann p3 book, p. 188 q 41

r= λi + (2λ-1)j-k
s= (1- λ ) i + 3λ j + (4λ-1)k
(a) find the values of λ for which r & s are perpendicular
when λ=2 r & s are the position vectors of the points A & B respectively.

b. Find AB

c. Use a scalar product to find the size of <BAO
(a) use dot product: λ(1- λ ) + (2λ-1)*(3λ) -1(4λ-1) = 0
now expand, simplify and solve the quadratic to get the possible values of 'λ'

(b) sub λ=2, to get A=2i + 3j - k, and B= -i + 6j + 7k
vector AB = B - A = -3i + 3j + 8k

(c) find the modulus of vecor AB, the modulus of vecor AO, and use the dot product formula:
AB . AO = |AB|.|AO|[email protected] ,where @ is the angle you want to find
0
14 years ago
#3
damnyou mockel!
0
14 years ago
#4
(Original post by mockel)
(a) use dot product: λ(1- λ ) + (2λ-1)*(3λ) -1(4λ-1) = 0
why does this come up? just to make it clear, the middle part says (2λ-1)* (3lamda)
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#5
thanks..
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14 years ago
#6
(Original post by mockel)
why does this come up? just to make it clear, the middle part says (2λ-1)* (3lamda)
It comes up because you haven't clicked the checkbox to disable smilies in that post :)
So, when you want lambda, and put &#955 ; (with no space before the ; ) and that is immediately followed by a ')', then it's interpreted as a smilie, viz. ;)
Disable smilies for a post and it'll come up ok.
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