This paper describes the main characteristics of the root lines of polynomials with complex coefficients. Root lines are defined as the geometric loci of the roots of the real, respective imaginary part of the polynomial. A graphical representation of these lines offers a clear picture of the positions of the polynomial's roots. The coordinates of various points of the root lines can be obtained by use of a computer program. Each root line leads to a given root, this way the polynomial can be solved and graphically represented. A short description of the rules of variation and properties of these root lines follows depending on the position of the roots of the polynomial. This study contains many numerical examples which show not only how the root lines, but also the polynomials with complex roots and coefficients work, how they can be studied, transformed and solved.
A. IntroductionThis study is a continuation and completion of a study about the root lines presented at the 27-th ARA Congress in Oradea, Romania, May 29 -June 2, 2002. The length of the study was then restricted to 5 pages, therefore some observations in the study could not be mathematically proved or demonstrated. This paper presents all those observations and new explanations regarding the properties of root lines.
B. Importance of the root lines.Root lines are characteristic for polynomials with complex roots. A polynomial of degree n has n roots and all roots can be complex. According to some scientific works the concept of complex roots has a particular importance to the physical and engineering sciences. See Reference [4] Volume II, for the list of such cases. The same [4], on page 413 and ff. also presents some curves which are root lines, but are called by the author μ(x,y) = c1 and ν(x,y) = c2. (μ and ν are obviously the real and imaginary part of the polynomial). The name "root lines"of this theory is given by me, and probably is not found in any other book or article. In the same chapter of that book [4] is also mentioned that the angles between these curves at a multiple root are equal. It explains this with the vector dot product of the gradients. This study gives a more simple explanation for this. The studies mentioned in [4] are also restricted to polynomials with real coefficients. My studies have no such restriction, because I found that they can easily be extended to cases with complex coefficients, so they are more general, without restriction.
C. The basic form of a polynomial isP n (w) = C n w n +C n-1 w n-1 + + C 1 x+ C 0( 1) w is the independent variable of the polynomial which can be a real or a complex number; regarding w see also Par. I. The coefficients C n to C 0 are complex or real numbers.
D. Roots of a polynomial.Roots (or zeros) of a polynomial are those values of the variable w for which the polynomial's value (both the real and the imaginary part) reduces to zero.
E. Real roots of a polynomial.If the variable w in relation (1) is a real number, and P(w) is represented along a straight reference line, then the roo...