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If v=3i+5j and w=-2i+2/3j, what is v*w?

 Dec 17, 2015
edited by gibsonj338  Dec 17, 2015

Best Answer 

 #4
avatar
+5

Solve for j:
6-8 i j+(10 j^2)/3 = 0

The left hand side factors into a product with four terms:
2/3 (-3 i+j) (3 i+5 j) = 0

Multiply both sides by 3/2:
(-3 i+j) (3 i+5 j) = 0

Split into two equations:
-3 i+j = 0 or 3 i+5 j = 0

Subtract -3 i from both sides:
j = 3 i or 3 i+5 j = 0

Subtract 3 i from both sides:
j = 3 i or 5 j = -3 i

Divide both sides by 5:
Answer: | j = 3 i         or j = -(3 i)/5
 

 Dec 18, 2015
 #1
avatar+8581 
0

What grade are you in, If you don't mind me asking??

 Dec 17, 2015
 #2
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I might help with your problem if you help with the problem that says home please help and explain

 Dec 17, 2015
 #3
avatar+495 
+5

v=√34 cis59.04°

w = 2√10/3 cis -18.43°

 

v*w = 2√10/3 * √34 cis59.04°-18.43°

 

= 12.293(cos40.61°)+i(sin40.61)

 

= 9.332i + 8.002j

 

*answer may be subject to rounding errors*

 

I might put all that in radical form later.

 Dec 17, 2015
 #4
avatar
+5
Best Answer

Solve for j:
6-8 i j+(10 j^2)/3 = 0

The left hand side factors into a product with four terms:
2/3 (-3 i+j) (3 i+5 j) = 0

Multiply both sides by 3/2:
(-3 i+j) (3 i+5 j) = 0

Split into two equations:
-3 i+j = 0 or 3 i+5 j = 0

Subtract -3 i from both sides:
j = 3 i or 3 i+5 j = 0

Subtract 3 i from both sides:
j = 3 i or 5 j = -3 i

Divide both sides by 5:
Answer: | j = 3 i         or j = -(3 i)/5
 

Guest Dec 18, 2015
 #5
avatar+33661 
0

I assume i and j are unit vectors in the x- and y-directions respectively and that a dot product is required for v.w.

 

If so, then i.i = i, j.j = j and i.j = j.i = 0  so:

 

(3i + 5j)(-2i + 2/3j) =   -6i.i + 2i.j - 10j.i +10/3j.j   =  -6i + 10/3j

 

If v*w is meant to be a cross product (vxw) then the third, z, dimension is involved and 

 

ixi = jxj = kxk = 0

ixj = -jxi = k

jxk = -kxj = i

kxi = -ixk = j

 Dec 20, 2015
edited by Alan  Dec 20, 2015

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