# help on factoring`

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#### Guest

##### Guest
i got this problem wrong and i did not know what i did wrong....

i was asked to factor 18+7x^2-x^4 and i factored it to (x^2+2)(x^2-9)

what did i do wrong????

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#### Guest

##### Guest
Hello!

do what you can......ummmm........keep trying factor it out and ummmm...whatever

#### JOSE JAIME-RODRIGUEZ

##### New member
You need one more step which is to simplify the factors:
(x^2-9) (x^2+2)....now you can finish it.

#### Chief343

##### New member
18+7x^2-x^4

Multiply by -1

x^4-7x^2-18

=(x^2-9)(x^2+2)

Factor, Difference of two squares x^2+-9

(x-3)(x+3)

Answer

(x^2+2)(x-3)(x+3)

#### soroban

##### Elite Member
Hello, brendaursula!

I was asked to factor $$\displaystyle 18\,+\,7x^2\,-\,x^4$$ and I factored it to $$\displaystyle (x^2\,+\,2)(x^2\,-\,9)$$

What did i do wrong?
Two things . . .

(1) If you multiply out your answer, you get: $$\displaystyle \,x^4\,-\,7x^2\,-\,18$$
$$\displaystyle \;\;\;$$which is not what they gave you.

(2) $$\displaystyle x^2\,-\,9$$ can be factored, so you aren't finished yet.

I suspect you factored by taking out a -1 first: $$\displaystyle \;-1(x^4\,-\,7x^2\,-\,18)$$

Then we get: $$\displaystyle \:-1(x^2\,+\,2)(x^2\,-\,9)$$

Replace the$$\displaystyle \,-1:\;\;(x^2\,+\,2)(\underbrace{9\,-\,x^2})$$
. . . . . . . . . . . . . . . . . . . . diff. of squares
. . . . . Answer: $$\displaystyle \x^2\,+\,2)\overbrace{(3\,-\,x)(3\,+\,x)}$$

#### ERIK VARGAS

##### New member
ok, you have(x^2+2) (X^2-9).
in your first set of parqantheses it is a differrnce of two squares and you cannot further find the square of 2.
( x^2-9) is a difference of two squares .
since 2 does not have a square find the square of negative nine which does have a square
(x^2+2) (x-3) (x+3) you will end up with this outcome