How do you write a polynomial function of least degree that has real coefficients, the following given zeros 8,-i, i and a leading coefficient of 1?

1 Answer
Nov 12, 2016

x^4-9x^3+9x^2-9x+8x49x3+9x29x+8

Explanation:

As the two zeros among four zeros, viz. 88, -ii, ii and 11 have two complex numbers, which are complex conjugate of each other, it is possible to write a polynomial function of least degree (which is 44 as there are 44 zeros with no multiplicity, i.e. repeat zeros) that has real coefficients.

A function f(x)f(x) with zeros aa, bb, cc and dd is (x-a)(x-b)(x-c)(x-d)(xa)(xb)(xc)(xd) and hence the function with 88, -ii, ii and 11as zeros, will be

(x-8)(x-(-i))(x+i)(x-1)(x8)(x(i))(x+i)(x1)

= (x-8)(x+i)(x-i)(x-1)(x8)(x+i)(xi)(x1)

= (x-8)(x-1)(x^2+ix-ix+(-i^2))(x8)(x1)(x2+ixix+(i2))

= (x-8)(x-1)(x^2+1)(x8)(x1)(x2+1) as i^2=-1i2=1

= (x^2-9x+8)(x^2+1)(x29x+8)(x2+1)

= x^4-9x^3+8x^2+x^2-9x+8x49x3+8x2+x29x+8

= x^4-9x^3+9x^2-9x+8x49x3+9x29x+8