How do you write a polynomial with zeros 4-i and sqrt(10)?

1 Answer
Aug 16, 2016

Answer:

This one works:

#x^2-(4+sqrt(10)-i)x+(4sqrt(10)-(sqrt(10))i)#

...but you probably want this one:

#x^4-8x^3+7x^2+80x-170#

Explanation:

If you allow coefficients of arbitrary type, then the polynomial of lowest degree with these zeros is simply:

#(x-(4-i))(x-sqrt(10))#

#= x^2-(4+sqrt(10)-i)x+(4sqrt(10)-(sqrt(10))i)#

If you want rational coefficients, then include the Complex conjugate #4+i# and the radical conjugate #-sqrt(10)# as two more zeros to find:

#(x-(4-i))(x-(4+i))(x-sqrt(10))(x+sqrt(10))#

#=((x-4)^2-i^2)(x^2-10)#

#=(x^2-8x+17)(x^2-10)#

#=x^4-8x^3+7x^2+80x-170#