Vector Direction Angles and Direction Cosines

[keepondlow]

If a vector has the given direction angles, find the third direction angle ?.
? = ?/4, ? = ?/3 , ? = ???

 

[Deleted member 4993]

If a vector has the given direction angles, find the third direction angle ?.
? = ?/4, ? = ?/3 , ? = ???

There is a cosine - square law - does that ring a bell?

 

[keepondlow]

yes..... Cos^2 (?) + Cos ^2 (?) + Cos^2 (?) = 1
and I found the angle for ? = ? because of the following: .5 + .25 + Cos^2 (?) = 1
My online homework says that ? not equal to ?

 

[Deleted member 4993]

yes..... Cos^2 (?) + Cos ^2 (?) + Cos^2 (?) = 1
and I found the angle for ? = ? <<< not necessarily true

\(\displaystyle cos(\gamma) = \pm \frac{1}{\sqrt{2}}\)

\(\displaystyle \gamma = \frac{\pi}{4} \, or \, \frac{3\pi}{4} \, or \, \frac{5\pi}{4} \, or \, \frac{7\pi}{4} [ = \, \pi ( \frac{1}{4} \pm n)]\)


because of the following: .5 + .25 + Cos^2 (?) = 1
My online homework says that ? not equal to ?