# Quick question on factor theorem Watch

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use the factor theorem to factorise the following cubics as far as possible:

f(x) = x^3 -7x-6

As there is no x^2 in the cubic do i need to first do algebraic division?

f(x) = x^3 -7x-6

As there is no x^2 in the cubic do i need to first do algebraic division?

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#2

(Original post by

use the factor theorem to factorise the following cubics as far as possible:

f(x) = x^3 -7x-6

As there is no x^2 in the cubic do i need to first do algebraic division?

**dippers**)use the factor theorem to factorise the following cubics as far as possible:

f(x) = x^3 -7x-6

As there is no x^2 in the cubic do i need to first do algebraic division?

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#3

If f(a) =0, then the algebraic expression has the factor (x-a). That's the factor theorem. Experiment with values of 1,-1,2,-2 etc to see what the factor is. Once you find this factor you can use algebraic division to find the others.

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(Original post by

See what the values of f(1) f(-1) etc You are looking for the value to be zero. This gives you your first factor.

**steve2005**)See what the values of f(1) f(-1) etc You are looking for the value to be zero. This gives you your first factor.

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#5

(Original post by

I did that then I did algrebraic division and got x^2-x-6, is this right? Then I'm not sure how to factorise it. I know you use (x+1) for the first bracket and i'm unsure how to do the rest.

**dippers**)I did that then I did algrebraic division and got x^2-x-6, is this right? Then I'm not sure how to factorise it. I know you use (x+1) for the first bracket and i'm unsure how to do the rest.

You could do long division OR synthetic division.

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I'm having problems with this question

I know I input 1 and -3/2 into the equation and then solve by doing simulataneous equations but I keep getting the wrong answer.

**Find a and b given that (x-1) and (2x+3) are factors of f(x)= ax^3+3x^2+bx-3.**I know I input 1 and -3/2 into the equation and then solve by doing simulataneous equations but I keep getting the wrong answer.

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#7

(Original post by

I'm having problems with this question

I know I input 1 and -3/2 into the equation and then solve by doing simulataneous equations but I keep getting the wrong answer.

**dippers**)I'm having problems with this question

**Find a and b given that (x-1) and (2x+3) are factors of f(x)= ax^3+3x^2+bx-3.**I know I input 1 and -3/2 into the equation and then solve by doing simulataneous equations but I keep getting the wrong answer.

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(Original post by

do you want to show your working

**TenOfThem**)do you want to show your working

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(Original post by

they are correct

**TenOfThem**)they are correct

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#11

(Original post by

How do i solve it from then, do i change the 0=a+b equation by multiplying by 3/2?

**dippers**)How do i solve it from then, do i change the 0=a+b equation by multiplying by 3/2?

Any method should be fine

Including the one you suggest

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(Original post by

There are many approaches to solving simultaneous equations

Any method should be fine

Including the one you suggest

**TenOfThem**)There are many approaches to solving simultaneous equations

Any method should be fine

Including the one you suggest

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#13

(Original post by

I still keep getting the wrong answer, i'm not sure why.

**dippers**)I still keep getting the wrong answer, i'm not sure why.

What do you get

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