operator [] method
Returns the coefficient of the polynomial at the given index
position.
For example:
final quadratic = Quadratic(
a: Complex.fromReal(2),
b: Complex.fromReal(-6),
c: Complex.fromReal(5),
);
final a = quadratic[0] // a = Complex(2, 0)
final b = quadratic[1] // b = Complex(-6, 0)
final c = quadratic[2] // c = Complex(5, 0)
An exception is thrown if the index
is negative or if it doesn't
correspond to a valid position.
Implementation
Complex operator [](int index) => coefficients[index];