Assuming that the maximum amplitude of the field at point O for a wave from midway between the slits is E(r), now find the magnitude of the combined...

Assuming that the maximum amplitude of the field at point O for a wave from midway between the slits is E(r), now find the magnitude of the combined field E at O due to the two slits. You may ignore variations in the maximum amplitude and consider only variations in phase of the waves emerging from the slits.Express your answer in terms of E(r), phi, and deltaphi.