Vector with angles with axis (book wrong?)

dimanche 30 mars 2014

1. The problem statement, all variables and given/known data



got a vector F (105,300,140)



magnitude: 347.3



it wants the angles, 3 of them with the axis x y z





2. Relevant equations



all my calculations has lead to the wrong answer, but the correct answer is (180-myanswer)



why is that?





3. The attempt at a solution



using AB = |A||b| cos α formula



so with an x-axis the coordinates are (1,0,0)



FX/|F||X|=cos(x-axis angle)



arcos(105/347.3) = x-axis angle



getting the answer: 72.4degrees



the "correct" answer is 107.6



meaning 180-72.4, why am i getting this 180degree descrepency?





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