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In algebra, a cubic equation in one variable is an equation of the form + + + = in which a is not zero. The ... which can be found by polynomial long division.
This method is especially useful for cubic polynomials, and sometimes all the roots of a higher-degree polynomial can be obtained. For example, if the rational root theorem produces a single (rational) root of a quintic polynomial , it can be factored out to obtain a quartic (fourth degree) quotient; the explicit formula for the roots of a ...
In mathematics, a cubic function is a function of the form () = + + +, that is, a polynomial function of degree three. In many texts, the coefficients a , b , c , and d are supposed to be real numbers , and the function is considered as a real function that maps real numbers to real numbers or as a complex function that maps complex numbers to ...
This polynomial is further reduced to = + + which is shown in blue and yields a zero of −5. The final root of the original polynomial may be found by either using the final zero as an initial guess for Newton's method, or by reducing () and solving the linear equation. As can be seen, the expected roots of −8, −5, −3, 2, 3, and 7 were ...
In mathematics, Ruffini's rule is a method for computation of the Euclidean division of a polynomial by a binomial of the form x – r. It was described by Paolo Ruffini in 1809. [ 1 ] The rule is a special case of synthetic division in which the divisor is a linear factor.
If P(x) has a rational root r, then P(x) is the product of x − r by a cubic polynomial in Q[x], which can be determined by polynomial long division or by Ruffini's rule. If there is a rational number α ≠ 0 such that α 2 is a root of R 3 (y), it was shown above how to express P(x) as the product of two quadratic polynomials in Q[x].
Completing the cube is a similar technique that allows to transform a cubic polynomial into a cubic polynomial without term of degree two. More precisely, if a x 3 + b x 2 + c x + d {\displaystyle ax^{3}+bx^{2}+cx+d}
All possible combinations of integer factors can be tested for validity, and each valid one can be factored out using polynomial long division. If the original polynomial is the product of factors at least two of which are of degree 2 or higher, this technique only provides a partial factorization; otherwise the factorization is complete.