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# Don't know where to start

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2. Let u = 2i − 5j and v = 10i − 25j. Find (a) u+v (b) u+1v 5 (c) u·v (d) a unit vector in the direction of u (e) Are u and v orthogonal?

Dec 3, 2015

#4
+111321
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a.  u + v   =  < 2i + 10i, -5j - 25j >   =   < 12i - 30j >

b.  This doesn't make any sense to me......

c.  u (dot) v  = ([2)(10)  + (-5)(-25)]   =  20 + 125  = 175

d.  The unit vector  is given by :   < 2 / sqrt [ 2^2 + (-5)^2]i , -5 / [ 2^2 + (-5)^2] j >   =

< 2/sqrt(29) i  , -5/sqrt(29) j >

e.  For the vectors to be orthogonal, the dot product would have to = 0......it was shown in (c) that this is not the case

Dec 3, 2015

#1
+109518
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I am really rusty on vectors - you'll have to wait for someone else :(

Dec 3, 2015
#3
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If you have time to write all that then you have time to do a quick internet search and send our guest to a net page that might be helpful.

OR you culd even just suggest this and give them a sensible word search suggestion like.

"How do I subtract vectors"  There are bound to be some great you tubes on it :)

Dec 3, 2015
#4
+111321
+15

a.  u + v   =  < 2i + 10i, -5j - 25j >   =   < 12i - 30j >

b.  This doesn't make any sense to me......

c.  u (dot) v  = ([2)(10)  + (-5)(-25)]   =  20 + 125  = 175

d.  The unit vector  is given by :   < 2 / sqrt [ 2^2 + (-5)^2]i , -5 / [ 2^2 + (-5)^2] j >   =

< 2/sqrt(29) i  , -5/sqrt(29) j >

e.  For the vectors to be orthogonal, the dot product would have to = 0......it was shown in (c) that this is not the case

CPhill Dec 3, 2015