Factoring Polynomials Help!

[cindib80]

I have watched my DVD and read the book and cannot figure this out.
I am factoring trinomialsof the form ax(squared)+bx+c

This is the one I am currently trying to decipher:
36x-3x(squared)-3x(cubed)

i just don't understand...

 

[stapel]

A good first step might be to write the polynomial in descending order, and then take out the common factor. Then factor the remaining quadratic.

Eliz.

 

[sgtpepper]

-3x^3 - 3x^2 + 36x

you can take a -3x out of everything:
3x(x^2 + x - 12)

then actually factor the the part in parenthesis:
leave aside the 3x for now:
(x^2 + x - 12) = (x + 4)(x - 3)
because x*x equals x^2 minus 3x plus 4x gives you 1x
so now you have x^2 + x (then - 12 from 4*-3)

x^2 + x - 12

so the answer I guess would be
3x[(x + 4)(x - 3)]

you can check it on InstaCalc. plug in any value for x and see how all three equations give you the same answer.

 

[stapel]

-3x^3 - 3x^2 + 36x

you can take a -3x out of everything:
3x(x^2 + x - 12)

If you take out a "-3x", then shouldn't there be a "-3x" in front (rather than a "+3x")?

Eliz.

 

[cindib80]

Thanks for everyone's help!

Thanks!