Iron filings line up along a magnet’s lines of ?

Iron filings trace out the lines of a magnetic field in three dimensions. Iron filings will line up parallel to a magnetic field, making the pattern of the field visible. This is a simple Snack to build—and because the filings are trapped in a bottle, they don't make a mess.

Explanation:

anchor = archer //

see the picture for the vector

the magnitude of the vector by pythagorean theorem

r = √( (-10)^2 + (3)^2 ) = √109

magnitude = √109 units

the direction angle between vector and x-axis is

tan^(-1)(3/10) = 16.699

so the direction is approximately 16.7 degrees north of west