Final answer:
The Pythagorean theorem can be used to calculate the length of a resultant vector when two vectors are at right angles to each other, as the vectors form the sides of a right-angled triangle with the resultant vector being the hypotenuse.
Step-by-step explanation:
The question is asking whether the Pythagorean theorem can be used to calculate the length of the resultant vector that is obtained when two vectors, which are at right angles to each other, are added. The correct answer to this question is 'a. True'. In a two-dimensional space, if two vectors are perpendicular to each other, then the magnitude of the resultant vector can indeed be calculated using the Pythagorean theorem, which states that in a right-angled triangle, the square of the length of the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the lengths of the other two sides. The two vectors form the sides of a right-angled triangle, and the resultant vector forms the hypotenuse.