What is the angle between #<0,5,4> # and #<5,-8,7>#?

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Answer 1 · 2015-12-21T21:43:47

#80,82^@#

The inner product of 2 vectors A and B in #RR^3# may be given by #A*B=||A|| ||B|| cos theta# where #theta# is the angle between A and B.

#therefore (0,5,4)*(5,-8,7)=||(0,5,4)|| *||(5,-8,7)|| cos theta#

#therefore theta = cos^(-1)((0-40+28)/(sqrt(0^2+5^2+4^2)*sqrt(5^2+8^2+7^2)))#

#=80,82^@#