Thread: angle between radius vector and x,y,z axis

1. angle between radius vector and x,y,z axis

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

Find the angle between radius vector of the point M(6,2,9) and:

a)x axis ; b)y axis ; c)z axis

2. Relevant equations

$cos(\vec{a},\vec{b})=\frac{\vec{a} \vec{b}}{|\vec{a}||\vec{b}|}$

3. The attempt at a solution

I tired with

$cos\alpha=\frac{(6,2,9)(6,0,0)}{\sqrt{121}\sqrt{36 }}$

but it is not like in my textbook results...

2. First off, there's no need to bother with a length 6 vector for the x-axis. The unit vector (1,0,0) will do nicely, and make things simpler to calculate.

Second, you haven't actually given the result of the calculation, which makes it difficult to see why it should be different from the textbook result.

Third, if you have cosine to the angle, it's fairly trivial to actually get the required result.

3. The results are for xy, xz, yz planes... Probably, its their typo fault when they were writing the task...

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