Question

Question #b4b92

Answer 1

Three angles

Explanation:

We live in three dimensional space. In a Cartesian coordinate system we need three coordinates to uniquely define a point in space, its `(x,y,z).`

Vector is defined as a quantity which has both magnitude and direction.

![http://intmstat.com]()
If `vecu` is a vector quantity, we need three angles which it makes with the three axes, as shown in the picture above, to uniquely define it.

If `alpha` is the angle between `vecu` and the `x`-axis,
`beta` is the angle between `vecu` and the `y`-axis and
`gamma` is the angle between `vecu` and the `z`-axis

Then unit vector `hatu` can be written as

`hatu = cos alpha hati + cos beta hatj + cosgamma hatk`

Where `hati, hatj and hatk` are unit vectors in `x,y,z` directions respectively.
And these three cosines are called the direction cosines.