If the accelerometer measures a total acceleration of 15 m/s^2 and an acceleration of 9 m/s^2 along the Y-axis, what is the acceleration along the X-axis?

Using the Pythagorean theorem, we can find the acceleration along the X-axis.
Acceleration along the X-axis = √(15^2 – 9^2)                       
                                                    = √144 = 12 m/s^2.