Answer:
90 degrees
Explanation:
In the attached image we can see, the condition where this condition (|A+B|=|A-B|) is true.
vector A is pointing horizontally to the right, vector B (positive), points up vertically.
Now analyzing the subtraction of vectors A and B = A - B, we have that vector A continues to point to the right (positive) and vector B points down (negative). In this way the magnitudes of both operations sum and subtraction of vectors is equal.
But the angle between the two vectors (A and B) will remain the same and will be 90°.