- #1

Karol

- 1,380

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Two lines A and B. The angle between them is θ, their direction cosines are (α,β,γ) and (α',β',γ'). Prove, ON GEOMETRIC CONSIDERATIONS:

##\cos\theta=\cos\alpha\cos\alpha'+\cos\beta\cos\beta'+\cos\gamma\cos\gamma'##

I posted this question long ago and i was told that this is the scalar product and i accepted then, but now i read further in the book and they explain the scalar product but still want the geometric proof.

##\cos\theta=\cos\alpha\cos\alpha'+\cos\beta\cos\beta'+\cos\gamma\cos\gamma'##

I posted this question long ago and i was told that this is the scalar product and i accepted then, but now i read further in the book and they explain the scalar product but still want the geometric proof.