Quaternion q = Quaternion.AxisAngle(new Vector3(1, 0, 0), Math.PI / 2);In this example, we create a quaternion that represents a rotation of 90 degrees around the x-axis. We use the Vector3 class to create a 3D vector with x=1, y=0, z=0, and Math.PI / 2 to represent an angle of 90 degrees. This method is part of the System.Numerics package in C#.