x^3 - 7x^2 - 14x + 120 ? Help please :(

Question

anonymous · Answer

u have to factoring?

shubhamsrg · Answer

You have to take the derivative of it? (I hope so)

kainui · Answer

We can't help unless you ask a question I'm afraid.

anonymous · Answer

Factorise

anonymous · Answer

synthetic division?

anonymous · Answer

do you know how to do it?

anonymous · Answer

I just need to know how to factorise it

anonymous · Answer

and i am telling you a way of doing it
so you dont know synthetic division
hmm
lets see

anonymous · Answer

I know how to do it when it's x^2 +x -a just not this one

anonymous · Answer

yes i got it
do you know rational root test?

anonymous · Answer

she leeeeft
sigh

anonymous · Answer

Let $\Large f(x)=x^3 - 7x^2 - 14x + 120=0$
$\Large f(x)$ has 3 roots: $\Large x=-4,5 $ and $\Large 6$
Thus, $\Large x^3 - 7x^2 - 14x + 120=(x+4)(x-5)(x-6)$

anonymous · Answer

^ ?

anonymous · Answer

@aajugdar What?

anonymous · Answer

That's right, but how did you work out that it's -4, 5 and 6?

anonymous · Answer

Just use $\Large Cardano\ Formula$: https://proofwiki.org/wiki/Cardano's_Formula

anonymous · Answer

idk this formula
but lol
looks complicated to me

anonymous · Answer

@BSwan  do you know this method?

anonymous · Answer

yeah , cardano lol
just apply the formula but there is much easier way from cardano :O

anonymous · Answer

factorize  120  to 6,-6,2,-2,4,-4,3,-3,5,-5,24,-24,12,-12,10,-10..
hehe and try f(x) that =0
if ur lucky u would find one of them :)
...
x^3 - 7x^2 - 14x + 120=(x-6)(x^2-x-20)