Marie Cornu, a physicist at the Polytechnic Institute in Paris, invented phasors in about 1880. This problem

Question:

Marie Cornu, a physicist at the Polytechnic Institute in Paris, invented phasors in about 1880. This problem helps you to see their utility. Find the amplitude and phase constant of the sum of two waves represented by the expressions
E1 = (12.0 kN/C) sin (15x - 4.5t)
And E2 = (12.0 kN/C) sin (15x - 4.5t + 70o)
(a) By using a trigonometric identity (as from Appendix B), and
(b) By representing the waves by phasors.
(c) Find the amplitude and phase constant of the sum of the three waves represented by
E1 = (12.0 kN/C) sin (15x - 4.5t + 70o),
E2 = (15.5 kN/C) sin (15x - 4.5t - 80o),
And E3 = (17.0 kN/C) sin (15x - 4.5t + 160 o)