Condition for this polynomial to be a perfect square

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SUMMARY

The condition for the polynomial x^4 + ax^3 + bx^2 + cx + d to be a perfect square is that it can be expressed as (x - α)^2(x - β)^2, where α and β are identical roots. This implies that the polynomial must be the product of two identical factors, specifically a quadratic polynomial squared, represented as (x^2 + mx + n)^2. Expanding this form allows for the comparison of coefficients to derive the necessary conditions on the coefficients a, b, c, and d.

PREREQUISITES
  • Understanding of polynomial expressions and their degrees
  • Knowledge of quadratic equations and their factorizations
  • Familiarity with the concept of perfect squares in algebra
  • Ability to expand polynomial expressions and compare coefficients
NEXT STEPS
  • Study the process of expanding (x^2 + mx + n)^2 to derive conditions on polynomial coefficients
  • Explore the implications of identical roots in polynomial equations
  • Learn about the characteristics of perfect squares in higher degree polynomials
  • Investigate the relationship between polynomial roots and their multiplicities
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Students studying algebra, particularly those focusing on polynomial functions and their properties, as well as educators seeking to explain the concept of perfect squares in polynomials.

utkarshakash
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Homework Statement


The condition that x^4+ax^3+bx^2+cx+d is a perfect square, is

Homework Equations



The Attempt at a Solution


If the above polynomial will be a perfect square then it can be represented as

(x-\alpha)^2(x-\beta)^2 where α and β are the roots of it.This means that two roots of it will be identical.
Am I correct in my assumption?
 
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utkarshakash said:

Homework Statement


The condition that x^4+ax^3+bx^2+cx+d is a perfect square, is

Homework Equations



The Attempt at a Solution


If the above polynomial will be a perfect square then it can be represented as

(x-\alpha)^2(x-\beta)^2 where α and β are the roots of it.This means that two roots of it will be identical.
Am I correct in my assumption?

Why do the 2 roots have to be identical? You've already shown what the general form of a quartic (degree 4 polynomial) needs to be in for it to be a perfect square, so go ahead and expand.

Although, I'd suggest you make the general form a general quadratic squared, so you'll have

(x^2+mx+n)^2

And once you expand this out, you can compare coefficients and find the conditions on a,b,c,d as required.
 
What does it mean to be a perfect square?

If the equation is quadratic ax^2+bx+c then it is a perfect square if it can be factored as (x+k)^2, ie two identical factors.

If you're starting with a fourth degree polynomial and you want to constrain it to be a perfect square then it must be the product of two identical factors. That factor must be a polynomial of degree 2 since you need an x^4 term when it is multiplied out. The most general form of a second degree polynomial is given above.
 

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