![]() ![]() Step 4 Check the solution in the original equation. This applies the above theorem, which says that at least one of the factors must have a value of zero. Since we have (x - 6)(x + 1) = 0, we know that x - 6 = 0 or x + 1 = 0, in which case x = 6 or x = - 1. ![]() Step 3 Set each factor equal to zero and solve for x. Solution Step 1 Put the equation in standard form. Of course, both of the numbers can be zero since (0)(0) = 0. We can never multiply two numbers and obtain an answer of zero unless at least one of the numbers is zero. We will not attempt to prove this theorem but note carefully what it states. In other words, if the product of two factors is zero, then at least one of the factors is zero. The method of solving by factoring is based on a simple theorem. This method cannot always be used, because not all polynomials are factorable, but it is used whenever factoring is possible. The simplest method of solving quadratics is by factoring. It is possible that the two solutions are equal.Ī quadratic equation will have two solutions because it is of degree two. This theorem is proved in most college algebra books.Īn important theorem, which cannot be proved at the level of this text, states "Every polynomial equation of degree n has exactly n roots." Using this fact tells us that quadratic equations will always have two solutions. The solution to an equation is sometimes referred to as the root of the equation. In other words, the standard form represents all quadratic equations. ![]() The standard form of a quadratic equation is ax 2 + bx + c = 0 when a ≠ 0 and a, b, and c are real numbers.Īll quadratic equations can be put in standard form, and any equation that can be put in standard form is a quadratic equation. Solve a quadratic equation by factoring.Ī quadratic equation is a polynomial equation that contains the second degree, but no higher degree, of the variable.Place a quadratic equation in standard form.Upon completing this section you should be able to: QUADRATICS SOLVED BY FACTORING OBJECTIVES You now have the necessary skills to solve equations of the second degree, which are known as quadratic equations. In previous chapters we have solved equations of the first degree. All skills learned lead eventually to the ability to solve equations and simplify the solutions. No such general formulas exist for higher degrees.Solving equations is the central theme of algebra. So in conclusion, there are only general formulae for 1st, 2nd, 3rd, and 4th degree polynomials. It's that we will never find such formulae because they simply don't exist. So it's not that we haven't yet found a formula for a degree 5 or higher polynomial. The Abel-Ruffini Theorem establishes that no general formula exists for polynomials of degree 5 or higher. In fact, the highest degree polynomial that we can find a general formula for is 4 (the quartic). Both of these formulas are significantly more complicated and difficult to derive than the 2nd degree quadratic formula! Here is a picture of the full quartic formula:īe sure to scroll down and to the right to see the full formula! It's huge! In practice, there are other more efficient methods that we can employ to solve cubics and quartics that are simpler than plugging in the coefficients into the general formulae. These are the cubic and quartic formulas. There are general formulas for 3rd degree and 4th degree polynomials as well. Similar to how a second degree polynomial is called a quadratic polynomial. A third degree polynomial is called a cubic polynomial. A trinomial is a polynomial with 3 terms. First note, a "trinomial" is not necessarily a third degree polynomial. ![]()
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