Question About Polynomials

Question About Polynomials

Postby Guest » Wed Jul 18, 2018 12:48 am

The equation Y=X^2 can be written as X^3 + PX^2 + Q = 0. Show that P=-1 and Q is equal to 20.

please help me solve this :)!
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Re: Question About Polynomials

Postby HallsofIvy » Fri Mar 08, 2019 10:26 am

Surely this isn't the whole question? If "X^2= Y" then X^3= XY so that X^3- YX+ 0= 0. The coefficient of X^2 and the constant term are 0.

If "X^3+ PX^2+ Q= 0" with P= -1 and Q= 20, so X^3- X^2+ 20= 0. If X= -2, X^3- X^2+ 20= -8- 4+ 20= 12. If X= -3, X^3- X^2+ 20= -27- 9+ 20= -16 so there is a root between -3 and -2. The other two roots are not real numbers. What does that have to do with "Y"?

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