In ch.3 of RHK book page 43-44, what is the difference between the
equation 13 and equation 15? They are both vector dot products.
Equation 13: a.b = ab cos(theta)
Equation 15: a.b = AxBx + AyBy + AzBz
On the coversheet homework, which one of the dot product equation am I
supposed to use?
Also, the difference between equation 16 and equation 17:
Equation 16: A x B = AB sin(theta)
Equation 17: A x B = (AyBz - AzBy)i + (AzBx - AxBz)j + (AxBy - AyBx)k
To solve the homework problems, which one of the equations should I use?
Equations 13 and 15 are completely equivalent. Use whichever one works best with the information that you have been given -- in the case of HW#2, you were given the vectors in component notation, so eqn.15 will probably be more useful. For the case of vectors in the x-y plane, there is a posting at: vectors showing how the two formulas are equivalent. Equations 16 and 17 are also completely equivalent, again the choice of which equation to use depends on what information you have been given about the vectors.