Factorise this Polynomial.

username1214428

Please help me factorise this polynomial. It is x³-10x²-x-30. I cannot figure out what x value will make this equal 0.

Reply 1

Serpentine111

Original post by VictoriaCoolio

Please help me factorise this polynomial. It is x³-10x²-x-30. I cannot figure out what x value will make this equal 0.

Is there more to this question? It doesn't factorise very nicely.

Reply 2

username1214428

Original post by Serpentine111

Is there more to this question? It doesn't factorise very nicely.

That's all my teacher gave us. She told us to try x= -2,-1,0,1,2.

Reply 3

plebianbob

It has a real root of 10.375, and a few complex roots as well, according to http://www.wolframalpha.com/input/?i=x3-10x2-x-30

Reply 4

Xabier

Original post by VictoriaCoolio

Please help me factorise this polynomial. It is x³-10x²-x-30. I cannot figure out what x value will make this equal 0.

What level is this aimed at? (e.g. GCSE, A Level..)

Reply 5

ThatPerson

Original post by VictoriaCoolio

Please help me factorise this polynomial. It is x³-10x²-x-30. I cannot figure out what x value will make this equal 0.

Is this meant to be trial and error?

Reply 6

username1214428

Original post by KingKumar

What level is this aimed at? (e.g. GCSE, A Level..)

Further Maths, so in between A Level and GCSE.

Reply 7

Iqbal007

Original post by VictoriaCoolio

Please help me factorise this polynomial. It is x³-10x²-x-30. I cannot figure out what x value will make this equal 0.

You know in further maths, at a-level you can use the calculator........the silver casio has a function where it'll tell you how to factorise up to X^3..........or you can use matlab :colone:

Reply 8

Serpentine111

Original post by VictoriaCoolio

That's all my teacher gave us. She told us to try x= -2,-1,0,1,2.

Are you sure you've typed out the question correctly then?

Reply 9

TheSK00T3R

The roots aren't even integers. Either the question is typed out wrong, or your teacher is giving you dodgy questions.

Reply 10

username1214428

Original post by Serpentine111

Are you sure you've typed out the question correctly then?

Definately, she might have made an error, she usually does. I just typed it in on a polynomial factoring calculator and it says this:
Result

x3−10x2−x−30=x3−10x2−x−30

Explanation

x3−10x2−x−30

cannot be factored because it has no rational zeroes.

Reply 11

Serpentine111

Original post by VictoriaCoolio

Definately, she might have made an error, she usually does. I just typed it in on a polynomial factoring calculator and it says this:
Result

x3−10x2−x−30=x3−10x2−x−30

Explanation

x3−10x2−x−30

cannot be factored because it has no rational zeroes.

She must've made a mistake then. There is 1 real root and 2 complex ones, but the answers aren't even integers.

In case you were interested: http://www.wolframalpha.com/input/?i=x^3-10x^2-x-30

No way is this A-level maths. I'm studying Physics at uni and I probably wouldn't be able to solve this.

Reply 12

username1214428

Original post by Serpentine111

This is GCSE Further Maths LOL. Our teacher hates us.

Reply 13

Serpentine111

Original post by VictoriaCoolio

This is GCSE Further Maths LOL. Our teacher hates us.

Hahaha, well it's definitely a mistake then.

Reply 14

username1214428

Original post by Serpentine111

Hahaha, well it's definitely a mistake then.

Thanks, I will ask her tomorrow.

Reply 15

Hasufel

As people on this post have pointed out, there is probably an error here.

Note however, that,

x^{3}-10x^{2}+x+30

DOES factorise. Try the lowest 2 factors of 30 (+/-1, +/-2)- the remaining quadratic (after division/synthetic division) can be factorised by the quadratic formula. (they are conjugates that involve a surd)