# Is this factorable???

#### JOSE JAIME-RODRIGUEZ

##### New member
The directions say to factor but I am not sure if the problem is factorable or not.Any directions or advice would be fully appreciated.

Here is the problem: 18+7x^2-x^4

Thank you for putting your time and effort in helping me with this problem.

#### skeeter

##### Senior Member
the expression is quadratic in x<sup>2</sup> ...

let u = x<sup>2</sup>

18 + 7x<sup>2</sup> - x<sup>4</sup> = 18 + 7u - u<sup>2</sup>

the right side will factor ... back substitute x<sup>2</sup> for u when you're done.

#### Denis

##### Senior Member
JOSE JAIME-RODRIGUEZ said:
The directions say to factor but I am not sure if the problem is factorable or not.Any directions or advice would be fully appreciated.
Here is the problem: 18+7x^2-x^4
Start by changing the signs (or multiplying by -1):
x^4 - 7x^2 - 18 ; now simply factor:
(x^2 - 9)(x^2 + 2)

#### JOSE JAIME-RODRIGUEZ

##### New member
Thank you Denis and Skeeter I could now finish this problem.Thank you for your help