Why nth Degree Equations Have n Roots?

In summary, an equation of nth degree is said to have n roots because for a polynomial P(x) of degree n, it has n complex roots (where n is a non-negative integer). This applies to all polynomials except for the single polynomial with degree not a non-negative integer (x^0=1). The Fundamental Theorem of Algebra states that every polynomial of degree n (n=/=0) has exactly n roots counting multiplicity over the Complex numbers, and for the real numbers, it has d roots where d is less than or equal to n. Nonzero polynomials of degree 0 have no solutions, and finding nth roots of complex numbers can be done algebraically or using polar form.
  • #1
johncena
131
1
Why is it said that an equation of nth degree must possesses n roots ?
if x^1 = y, x has only 1 value
x^2 = y, x has 2 values (the 2 values may be equal)
x^3 = y, x has 3 values
going on like this, we have, x^0 = 1 , implies x has no solutions. but x has infinite number of solutions.
 
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  • #2
What people say when they say that an equation of degree n has n roots is that given a polynomial P(x) of degree n, it has n complex roots (where n is a non-negative integer). However x^0=1 so the polynomial in your last example is:
P(x) = x^0 - 1 = 1-1 = 0
This does not have degree 0. We often say that it has degree [itex]-\infty[/itex], but since it's the only polynomial with degree not a non-negative integer this is the single polynomial to which the rule does not apply.
 
  • #3
Fundamental Theorem of Algebra: Every polynomial of degree n (n=/=0) has exactly n roots counting multiplicity over the Complex numbers. In the case of the real numbers, it has d roots where d is less than or equal to n.
For instance, the easiest example x^2+1=0 only has complex solutions, namely i and -i, but over the Reals, it has no roots.
Now to finish your question consider nonzero polynomials of degree 0, suggesting they are nonzero, they have no solutions. E.g., f(x)=5 is a polynomial of degree 0 and has 0 roots.
 
  • #4
I guess [itex]x^{1/2} = 4[/itex] has half a solution!
 
  • #5
g_edgar said:
I guess [itex]x^{1/2} = 4[/itex] has half a solution!
I'm assuming that you're joking, as this would not be a polynomial in the first place. The Fundamental Theorem of Algebra applies to non-constant single-variable polynomials with complex coefficients.

I don't know why, but finding nth roots of complex numbers is one of my favorite topics in teaching Pre-Calculus. I find it fascinating to see that you can find nth roots algebraically (like, for instance solving the equation [tex]x^{4}-1=0[/tex] to find the fourth roots of unity), or by using polar form ([tex]1 = cos 0 + i sin 0[/tex]) and get the same answers. I usually get a 'wow' moment from my students when I show them this.


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FAQ: Why nth Degree Equations Have n Roots?

Why do nth degree equations have n roots?

Nth degree equations have n roots because of the fundamental theorem of algebra, which states that a polynomial equation of degree n has n complex roots. This means that for every degree of an equation, there will be a corresponding number of solutions or roots.

How do I find the roots of an nth degree equation?

To find the roots of an nth degree equation, you can use various methods such as factoring, completing the square, or using the quadratic formula. For higher degree equations, you can also use numerical methods like Newton's method or the bisection method.

Can an nth degree equation have more than n roots?

No, an nth degree equation can only have n roots. This is because of the fundamental theorem of algebra, which states that the number of complex roots of a polynomial equation is equal to its degree. However, some of these roots may be repeated or have a multiplicity greater than 1.

Why are nth degree equations important?

Nth degree equations are important in many fields of science and mathematics, including physics, engineering, and economics. They are used to model various real-world phenomena and make predictions about the behavior of systems. They also have practical applications in solving problems involving calculations, optimization, and data analysis.

How does the degree of an equation affect its number of roots?

The degree of an equation directly affects the number of roots it has. As the degree increases, the number of roots also increases. For example, a quadratic equation (degree 2) has 2 roots, while a cubic equation (degree 3) has 3 roots. This is due to the fundamental theorem of algebra, which states that the number of complex roots is equal to the degree of the polynomial equation.

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