When the two simple harmonic motions have dissimilar amplitudes and also vary in phase but they have the similar periodic time :

The resultant curve may be obtained graphically in the above manner. Its shape will be found to vary with different phase differences as shown in figure. It is to be noted that the resultant value' figure in this case is generally an ellipse, the eccentricity and the inclination of which depend on the two amplitudes and the phase dissimilarity. When the phase difference is zero or Π, the ellipse changes to  a straight line.