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These 3 cosines are called the direction cosines. Then we can use the scalar product and write: Γ is the angle between u and the z-axis (in pink),

Β is the angle between u and the y-axis (in green) and Α is the angle between u and the x-axis (in dark red),

We now zoom in on the vector u, and change orientation slightly, as follows: On the graph, u is the unit vector (in black) pointing in the same direction as vector OA, and i, j, and k (the unit vectors in the x-, y- and z-directions respectively) are marked in green. (Go here for a reminder on unit vectors). Suppose also that we have a unit vector in the same direction as OA. Suppose we have a vector OA with initial point at the origin and terminal point at A.