| a | = 4； Then a is either -4 or = 4;

| b | = 3； Then a is either -3 or = 3;

& lta, b>= 30 is a completely confusing topic;

Then a*b is only = 12.

Extended data

Negative vector

If the modulus of vector AB and vector CD are equal and the directions are opposite, then we call vector AB the negative vector of vector CD, which is also called the inverse vector.

Zero vector

A vector with a length of 0 is called a zero vector and recorded as 0. The starting point and ending point of the zero vector coincide, so the zero vector has no definite direction, or the direction of the zero vector is arbitrary.

Equal vector

Vectors with the same length and direction are called equal vectors. Vectors a and b are equal, so let's say a = b. ..

Rule: All zero vectors are equal.

When the vector is represented by a directed line segment, the starting point can be arbitrarily selected. Any two equal nonzero vectors can be represented by the same directed line segment, regardless of the starting point of the directed line segment. Directed line segments with the same direction and length all represent the same vector.