Determine the angle that vector a= (12,-3,4) makes with the y-axis.

Answer 1

A vector B along y axis could be 0i + 1 j + 0 k
Then what is A dot B ?
B = 0 i + 1 j + 0 k
A = 12i - 3 j + 4 k

A dot B = 0 -3 + 0 = -3
|A| = sqrt (144+9+16)
|B| = 1
cos (T) = -3/(|A||B|)