Answer:
The mathematical expression is
Explanation:
Given if we know the components of a vector, then we have to find what mathematical relationship can be used to find the magnitude of the vector.
In two-dimensional coordinate system, any vector can be broken into two components x and y -component.

The vector v and its components horizontal and vertical components form a right angled triangle as shown in attachment below.
Using the Pythagoras Theorem in the right triangle

⇒

The above mathematical relationship can be used to find the magnitude of the vector.