A and B are real numbers, and | a b |≤| a |+b| and | a b |≥| a |-b | are called trigonometric inequalities.

Changing real numbers A and B into vectors is called triangle inequality in vector form.

When vector A and vector B are not linear, vector A, vector B and vector A B can form a triangle, where | A B | is the length of one side, while | A |+B | and ||a|-|b|| are the sum and difference of two sides, and the sum of two sides of a triangle is greater than the third side, and the difference between the two sides is smaller than the third side.

Therefore, the triangle inequality in vector form holds.