MATLAB: How to expand fully with complex numbers

complex numbersfoil expansionimaginary numbers

Hello all,

Might be a rookie question but I am wondering how to do FOIL multiplication with complex numbers. This far I've managed to get something displaying a polynomial As^4 + Bs^3 + Cs^2 + … , however all coefficients are complex numbers and I would like the imaginary components of these to cancel out as they do when performing this by hand.

Even a point in the right direction would be appreciated!

Best Answer

clear all %an example
syms x
polynomial=i*x-x.^2 %i indicates imaginary number
a = coeffs(polynomial)
real(a)

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MATLAB: Real Roots of a Polynomial

Use 'roots' to find the roots of polynomials.

 r = roots([1,7,-8,5,1]); % Get all the roots
 r = r(imag(r)==0); % Save only the real roots

The 'isreal' function is true only if All elements of a vector are real, so it isn't appropriate for sorting out the real roots.

A polynomial with all real coefficients such as yours cannot have an odd number of complex roots. They must occur in conjugate pairs. As you see, in your particular polynomial there are just two complex roots, which are conjugates of one another.

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   >> doc repmat

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MATLAB: Real Roots of a Polynomial

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