Having an issue with Undefined symbols

I am receiving this error in the build log, I can see it is a linking error, but all of the functions are defined in their necessary .cpp files and declared in the relevant header file.

*** Using Compiler 'V5.06 update 3 (build 300)', folder: 'C:\Keil_v5\ARM\ARMCC\Bin'
Build Project 'Game' - Target 'NXP LPC4088'
linking...
.\Objects\Game.axf: Error: L6218E: Undefined symbol Vector::Vector(float, float, float) (referred from matrix3x3.o).
.\Objects\Game.axf: Error: L6218E: Undefined symbol Vector::Vector() (referred from quaternion.o).
.\Objects\Game.axf: Error: L6218E: Undefined symbol Vector::operator /=(float) (referred from quaternion.o).
.\Objects\Game.axf: Error: L6218E: Undefined symbol Quaternion::Magnitude() (referred from physics.o).
.\Objects\Game.axf: Error: L6218E: Undefined symbol Quaternion::operator /=(float) (referred from physics.o).
.\Objects\Game.axf: Error: L6218E: Undefined symbol Quaternion::operator +=(Quaternion) (referred from physics.o).
.\Objects\Game.axf: Error: L6218E: Undefined symbol Vector::Reverse() (referred from physics.o).
.\Objects\Game.axf: Error: L6218E: Undefined symbol Vector::Magnitude() (referred from physics.o).
.\Objects\Game.axf: Error: L6218E: Undefined symbol Vector::Normalise() (referred from physics.o).
.\Objects\Game.axf: Error: L6218E: Undefined symbol Vector::operator -=(Vector) (referred from physics.o).
.\Objects\Game.axf: Error: L6218E: Undefined symbol Vector::operator -() (referred from physics.o).
.\Objects\Game.axf: Error: L6218E: Undefined symbol Vector::operator +=(Vector) (referred from physics.o).
.\Objects\Game.axf: Error: L6218E: Undefined symbol Matrix3x3::Inverse() (referred from physics.o).
.\Objects\Game.axf: Error: L6218E: Undefined symbol Matrix3x3::Transpose() (referred from physics.o).
.\Objects\Game.axf: Error: L6218E: Undefined symbol Matrix3x3::Matrix3x3() (referred from physics.o).
Not enough information to list image symbols.
Finished: 1 information, 0 warning and 15 error messages.
".\Objects\Game.axf" - 15 Error(s), 0 Warning(s).
Target not created.
Build Time Elapsed:  00:00:00

Here is the Vector.h class as an example:

#ifndef VECTOR_H
#define VECTOR_H

//Vector Class definition and function prototypes
class Vector{
        public:
                float x;
                float y;
                float z;


        Vector(void);
        Vector(float xi, float yi, float zi);

        float Magnitude(void);
        void Normalise(void);
        void Reverse(void);

        Vector& operator+=(Vector u);
        Vector& operator-=(Vector u);
        Vector& operator*=(float s);
        Vector& operator/=(float s);

        Vector operator-(void);
};

#endif

and here is an example of some of the Vector.cpp

#include <math.h>
#include "Vector.h"


//--------------------------------------------------------------------------------------------------------------------------------------
//Vector member functions
//--------------------------------------------------------------------------------------------------------------------------------------

//Constructor no arguments
inline Vector::Vector(void)
{
        x=0;
        y=0;
        z=0;
}

//Constructor with defined arguments
inline Vector::Vector(float xi, float yi, float zi)
{
        x=xi;
        y=yi;
        z=zi;
}

//Magnitude
inline float Vector::Magnitude(void)
{
        return(float) sqrt(x*x + y*y +z*z);
}

//Normalise
inline void Vector::Normalise(void)
{
        float const tol = 0.0001f;
        float m = (float) sqrt(x*x + y*y +z*z);
        if(m<=tol) m=1;
        x /= m;
        y /= m;
        z /= m;

        if(fabs(x) < tol) x = 0.0f;
        if(fabs(y) < tol) y = 0.0f;
        if(fabs(z) < tol) z = 0.0f;
}

Please tell me if I've made a stupid mistake but I feel as though I can't progress past this error alone.