Answer:
C. 142°
Step-by-step explanation:
You want the angle between vectors u=3i+√3j and v=-2i-5j.
Angle
There are a number of ways the angle between the vectors can be found. For example, the dot-product relation can give you the cosine of the angle:
u•v = |u|·|v|·cos(θ) . . . . . . where θ is the angle of interest
You can find the angles of the vectors individually, and subtract those:
u = |u|∠α
v = |v|∠β
θ = α - β
When the vectors are expressed as complex numbers, the angle between them is the angle of their quotient:
[tex]\dfrac{\vec{u}}{\vec{v}}=\dfrac{|\vec{u}|\angle\alpha}{|\vec{v}|\angle\beta}=\dfrac{|\vec{u}|}{|\vec{v}|}\angle(\alpha-\beta)=\dfrac{|\vec{u}|}{|\vec{v}|}\angle\theta[/tex]
This method is used in the calculation shown in the first attachment. The angle between u and v is about 142°.
A graphing program can draw the vectors and measure the angle between them. This is shown in the second attachment.
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Additional comment
The approach using the quotient of the vectors written as complex numbers is simply computed using a calculator with appropriate complex number functions. There doesn't seem to be any 3D equivalent.
The dot-product relation will work with 3D vectors as well as 2D vectors.
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