Find the resultant vector (mag and dir) given the following information: A. Ax = 5.7, Ay = 3.4

A two-dimensional vector is a geometrical object that can be given either as a magnitude and direction, or as two components. When the two components are given, as in this problem, the magnitude and direction can be determined by using Pythagorean Theorem.
The x- and y- components of the vector, together with the vector itself, form a right triangle, in which the vector is the hypotenuse. The length of the hypotenuse is the magnitude of the vector. It equals
A = sqrt(A_x^2 + A_y^2) = sqrt(5.7^2 + 3.4^2)= 6.6
The direction is usually given as an angle that the vector makes with the x-axis. This angle is adjacent to the x-component and opposite to the y-component. Then, it equals to the inverse tangent (arctangent) of the ratio of the components.
tan^(-1)(A_y/A_x) = tan^(-1)(3.4/5.7) = 31 degrees.
Therefore, the given vector A has the magnitude of 6.6 units and it makes the angle of 31 degrees with the positive direction of x-axis.
https://www.physicsclassroom.com/class/vectors/Lesson-1/Vector-Resolution