Question

(X+4) is a factor of x3-13x+12.find the other roots.

Answer 1

How do you factorise x^3-13x-12?

Hey, I just met 
and this is crazy, 
I'm doing a maths project, 
so, help me maybe?

6 answers · Mathematics 

 Best Answer

The first thing you look at are the factors of the constant (the term with no x's) 
these are 1, 2, 3, 4, 6 and 12 
You know that x = 1 won't be a root, (1 - 13 - 12 is not 0) 
but x = -1 gives (-1 + 13 - 12 = 0) so (x+ 1) is a factor 
You can also check -3 ( -27 + 39 -12 = 0) 
and x = 4...(64 - 52 - 12 = 0) 
and so: 
x^3 - 13x - 12 = (x+ 1)(x - 4)(x + 3)

L. E. Gant · 7 years ago

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x^3-13x-12 => by rational root theorem possible rational roots are: ± 1 , ± 2 , ± 3 , ± 4 , ± 6 , ± 12 => by inspection i.e. f(c) = 0, determine , x... show more

iceman · 7 years ago

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x^3 -13 x- 12 
= ( x +1 ) ( x^2 - x-12) 
= (x+1) { x^2 - 4x + 3x -12 } 
= (x+1) { x(x- 4) + 3( x- 4) } 
= (x+1 ) ( x-4) (x+ 3) ANSWER

Rameshwar · 7 years ago

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Here x=4 makes the polynomial zero. therefore, x - 4 is a factor of this polynomial... Now divide this polynomial with x - 4. You will get a quadratic... show more

Rupkatha · 7 years ago

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(x+1)*(x+3)*(x-4)