Calculating Magnitude of Vector Product of Two Vectors

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To find the magnitude of the vector product of two vectors, the formula used is |A| * |B| * sin(alpha). The user initially calculated the product using cosine instead of sine, leading to incorrect results. They mistakenly assumed the angle alpha was 60 degrees and later tried 120 degrees, both of which were incorrect. The correct approach involves using the sine of the angle between the vectors, not cosine. Clarification on the use of sine in the vector product calculation is needed for accurate results.
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Homework Statement


For the two vectors in the figure , find the magnitude of the vector product lAl x lBl.
http://session.masteringphysics.com/problemAsset/1040325/3/yf_Figure_1_29.jpg

Homework Equations


lAl*lBl=lAl*lBlsin(alpha)


The Attempt at a Solution



2.8cm * 1.9cm * cos(60) = 2.66cm^2

2.8cm * 1.9cm * cos(120) = -2.66cm^2

Since they made two 60 degree, I thought the alpha was 60 but I got wrong.

Then, I came up with the 120 degree, however it is also wrong.

Where did I do wrong?

Please help me..
 
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Why do you use cosine 120 degrees instead of sine?

ehild
 

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