Explanation

The dot product of a vector with itself is equal to the square of its magnitude, or |A|².

The dot product of two vectors A and B is defined as: A · B = |A| |B| cos θ, where θ is the angle between the vectors.

When a vector is dotted with itself, the angle θ becomes 0 (since the vectors are parallel), and cos 0 = 1.

Therefore, A · A = |A| |A| cos 0 = |A|².