According to the query of Baidu question bank, the modules of opposite vectors are equal, because they are mathematically defined as vectors with the same length but opposite directions. The length or modulus of a vector refers to the distance of the vector from the origin to the destination, so the modulus of the opposite vector is equal.

For example, given the directional quantity A, if there is a vector X that makes a+x=0, then X is called the inverse quantity of A, which means A+(-a) = 0. According to the definition of vector addition, A and -a are equal in length and opposite in direction, and A and -a are vectors with opposite directions.