- #1
tamtam402
- 201
- 0
Homework Statement
Using these 2 vectors:
[itex] \vec u = (3,-4,0)[/itex]
[itex] \vec v = (1,1,1)[/itex]
I must verify that theta is the same with these 2 equations:
Dot product
[itex] \vec u \bullet \vec v = ||\vec u|| ||\vec v|| cos( \theta)[/itex]
Cross product
[itex] ||\vec u \wedge \vec v|| = ||\vec u|| ||\vec v|| sin( \theta)[/itex]
Homework Equations
They were given in 1)
The Attempt at a Solution
I did all the calculations, I get the following answers:
[itex] ||\vec u || = 5[/itex]
[itex] ||\vec v || = \sqrt{3}[/itex]
[itex] \vec u \bullet \vec v = -1[/itex]
[itex] ||\vec u \wedge \vec v|| =\sqrt{74}[/itex]I then solve the 2 equations given above using arcsin and arccos to find the values of theta, but I get 96.6 using the dot product, and 83.3 using the cross product. The weird thing is that 180-83.3 = 96.6...
I must be missing something obvious, but I can't understand why I get the wrong answer :(