Final answer:
The magnitude of the resultant vector is found using the Pythagorean theorem.
Step-by-step explanation:
When two vectors are at right angles to each other, the magnitude of their resultant vector can be found using the Pythagorean theorem. The magnitude of the resultant vector is the square root of the sum of the squares of the magnitudes of the individual vectors. In this case, if vector a has a magnitude of 5.00 units and vector b is at right angles to vector a, then the magnitude of the resultant vector would be sqrt(5.002 + 02) = 5.00 units. Since vector b is at right angles to vector a, its magnitude does not contribute to the magnitude of the resultant vector.