How do you find all zeros for x^3 - 5x^2 + x - 5x35x2+x5?

1 Answer
May 17, 2016

x =5x=5
or
x=+-ix=±i

Explanation:

x^3-5x^2+x-5x35x2+x5 can be factored as
color(white)("XXX")color(red)(""(x^3+x))-color(blue)(""(5x^2+5))XXX(x3+x)(5x2+5)

color(white)("XXX")=color(red)(x(x^2+1))-color(blue)(5(x^2+1)XXX=x(x2+1)5(x2+1)

color(white)("XXX")=(color(red)(x)-color(blue)(5))*(x^2+1)XXX=(x5)(x2+1)

For the zeroes:
either
color(white)("XXX")(x-5)=0color(white)("XX")rarrcolor(white)("XX")x=5XXX(x5)=0XXXXx=5
or
color(white)("XXX")(x^2+1)=0color(white)("XX")rarrcolor(white)("XX")x=+-sqrt(-1)=+-iXXX(x2+1)=0XXXXx=±1=±i