It is known that a is the unit vector in the plane. If B satisfies b * (a-b) = 0, then the value range of the module of B is? Why not - 1 ≤| B | ≤ 1

It is known that a is the unit vector in the plane. If B satisfies b * (a-b) = 0, then the value range of the module of B is? Why not - 1 ≤| B | ≤ 1

B * (a-b) = 0, which is a fallible problem, including the following cases: 1. B is a zero vector, 2. A-B is a zero vector, 3. B and A-B are not zero vectors, then B is perpendicular to a-b. in this case, as long as the modulus of vector a is greater than 0, it can be solved by the triangle rule