The polynomial f(x) is given by f(x) = x^3 + 4x -5(adsbygoogle = window.adsbygoogle || []).push({});

show x-1 is factor :

f(1)=0

1+4-5=0 Thus it's a factor.

express in form (x-1)(x^2+px+q)

ends up being X^2 + X + 5.

next question is :

hence show the equation f(x) = 0 has one real root state it's value.

i know i have to use b^2 -4ac. If i do that it's -19 which is <0 so it's 1 value. But how do I find the value. And why does all this stuff work.

My teacher is one that just tells you how to do it. I have no idea why i'm doing it and it makes no sense so it's harder to remember. I would get 1or 2 marks out of 3 for this.

Firstly i dont know how to find out what the real number is. and i don't know why this works.

explain plez?! 8D

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Given f(x) = x^3 + 4x -5, show x-1 is a factor

**Physics Forums | Science Articles, Homework Help, Discussion**