# Need Help ASAP!!

• Sep 30th 2007, 03:07 PM
rsultana
Need Help ASAP!!
Can someone help me with this problem please:
finding all real numbers:
1. x4 - 3x3 + 2 = 0
oh and if i have a problem with square root how do i type it in here??
• Sep 30th 2007, 03:20 PM
Jhevon
Quote:

Originally Posted by rsultana
Can someone help me with this problem please:
finding all real numbers:
1. x4 - 3x3 + 2 = 0
oh and if i have a problem with square root how do i type it in here??

trying the factors of 2, we realize that x = 1 is a root. thus by the factor theorem, (x - 1) is a factor.

so, performing long division of polynomials (or synthetic division), we realize that:

$\left( x^4 - 3x^3 + 2 \right) \div (x - 1) = x^3 - 2x^2 - 2x - 2$

so we have: $x^4 - 3x^3 + 2 = (x - 1) \left( x^3 - 2x^2 - 2x - 2 \right)$

the cubic has no rational solution. the one real solution it has is irrational, so it would be hard to find the root for that one. you can use the quadratic formula, or if you are in calculus. you can guess a real root and then refine it using Newton-Raphson method.

to type square root of something, say x, you type: sqrt(x)

or you can learn LaTex

EDIT: oh, you're in middle school. well...this is an unfair question :D
i don't recall being able to solve a cubic like that in middle school
• Sep 30th 2007, 03:25 PM
rsultana
Quote:

Originally Posted by Jhevon
trying the factors of 2, we realize that x = 1 is a root. thus by the factor theorem, (x - 1) is a factor.

so, performing long division of polynomials (or synthetic division), we realize that:

$\left( x^4 - 3x^3 + 2 \right) \div (x - 1) = x^3 - 2x^2 - 2x - 2$

so we have: $x^4 - 3x^3 + 2 = (x - 1) \left( x^3 - 2x^2 - 2x - 2 \right)$

the cubic has no rational solution. the one real solution it has is irrational, so it would be hard to find the root for that one. you can use the quadratic formula, or if you are in calculus. you can guess a real root and then refine it using Newton-Raphson method.

to type square root of something, say x, you type: sqrt(x)

or you can learn LaTex

EDIT: oh, you're in middle school. well...this is an unfair question :D
i don't recall being able to solve a cubic like that in middle school

no actually i didnt see that his section was for middle school...lolz...m in college so i went and posted it in college section...thnx :D