2.6 Other types of equations (Page 4/10)

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Solve the absolute value equation: $| 1 - 4 x | + 8 = 13.$

$x = −1,$ $x = \frac{3}{2}$

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Solving other types of equations

There are many other types of equations in addition to the ones we have discussed so far. We will see more of them throughout the text. Here, we will discuss equations that are in quadratic form, and rational equations that result in a quadratic.

Solving equations in quadratic form

Equations in quadratic form are equations with three terms. The first term has a power other than 2. The middle term has an exponent that is one-half the exponent of the leading term. The third term is a constant. We can solve equations in this form as if they were quadratic. A few examples of these equations include $x^{4} - 5 x^{2} + 4 = 0, x^{6} + 7 x^{3} - 8 = 0,$ and $x^{\frac{2}{3}} + 4 x^{\frac{1}{3}} + 2 = 0.$ In each one, doubling the exponent of the middle term equals the exponent on the leading term. We can solve these equations by substituting a variable for the middle term.

A General Note

Quadratic form

If the exponent on the middle term is one-half of the exponent on the leading term, we have an equation in quadratic form , which we can solve as if it were a quadratic. We substitute a variable for the middle term to solve equations in quadratic form.

How To

Given an equation quadratic in form, solve it.

Identify the exponent on the leading term and determine whether it is double the exponent on the middle term.
If it is, substitute a variable, such as u , for the variable portion of the middle term.
Rewrite the equation so that it takes on the standard form of a quadratic.
Solve using one of the usual methods for solving a quadratic.
Replace the substitution variable with the original term.
Solve the remaining equation.

Solving a fourth-degree equation in quadratic form

Solve this fourth-degree equation: $3 x^{4} - 2 x^{2} - 1 = 0.$

This equation fits the main criteria, that the power on the leading term is double the power on the middle term. Next, we will make a substitution for the variable term in the middle. Let $u = x^{2} .$ Rewrite the equation in u .

3 u^{2} - 2 u - 1 = 0

Now solve the quadratic.

\begin{matrix} 3 u^{2} - 2 u - 1 & = & 0 \\ (3 u + 1) (u - 1) & = & 0 \end{matrix}

Solve each factor and replace the original term for u.

\begin{matrix} 3 u + 1 & = & 0 \\ 3 u & = & −1 \\ u & = & - \frac{1}{3} \\ x^{2} & = & - \frac{1}{3} \\ x & = & \pm i \sqrt{\frac{1}{3}} \end{matrix}

\begin{matrix} u - 1 & = & 0 \\ u & = & 1 \\ x^{2} & = & 1 \\ x & = & ±1 \end{matrix}

The solutions are $\pm i \sqrt{\frac{1}{3}}$ and $\pm 1.$

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Try It

Solve using substitution: $x^{4} - 8 x^{2} - 9 = 0.$

$x = −3, 3, - i, i$

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Solving an equation in quadratic form containing a binomial

Solve the equation in quadratic form: ${(x + 2)}^{2} + 11 (x + 2) - 12 = 0.$

This equation contains a binomial in place of the single variable. The tendency is to expand what is presented. However, recognizing that it fits the criteria for being in quadratic form makes all the difference in the solving process. First, make a substitution, letting $u = x + 2.$ Then rewrite the equation in u.

\begin{matrix} u^{2} + 11 u - 12 & = & 0 \\ (u + 12) (u - 1) & = & 0 \end{matrix}

Solve using the zero-factor property and then replace u with the original expression.

\begin{matrix} u + 12 & = & 0 \\ u & = & −12 \\ x + 2 & = & −12 \\ x & = & −14 \end{matrix}

The second factor results in

\begin{matrix} u - 1 & = & 0 \\ u & = & 1 \\ x + 2 & = & 1 \\ x & = & −1 \end{matrix}

We have two solutions: $−14,$ and $−1.$

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Try It

Solve: ${(x - 5)}^{2} - 4 (x - 5) - 21 = 0.$

$x = 2, x = 12$

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Solving rational equations resulting in a quadratic

Earlier, we solved rational equations. Sometimes, solving a rational equation results in a quadratic. When this happens, we continue the solution by simplifying the quadratic equation by one of the methods we have seen. It may turn out that there is no solution.

Questions & Answers

Ayele, K., 2003. Introductory Economics, 3rd ed., Addis Ababa.

Widad Reply

can you send the book attached ?

Ariel

What is economics

Widad Reply

the study of how humans make choices under conditions of scarcity

AI-Robot

U(x,y) = (x×y)1/2 find mu of x for y

Desalegn Reply

U(x,y) = (xÃy)1/2 find mu of x for y

Desalegn

what is ecnomics

Jan Reply

this is the study of how the society manages it's scarce resources

Belonwu

what is macroeconomic

John Reply

macroeconomic is the branch of economics which studies actions, scale, activities and behaviour of the aggregate economy as a whole.

husaini

etc

husaini

difference between firm and industry

husaini Reply

what's the difference between a firm and an industry

Abdul

firm is the unit which transform inputs to output where as industry contain combination of firms with similar production 😅😅

Abdulraufu

Suppose the demand function that a firm faces shifted from Qd  120 3P to Qd  90  3P and the supply function has shifted from QS  20  2P to QS 10  2P . a) Find the effect of this change on price and quantity. b) Which of the changes in demand and supply is higher?

Toofiq Reply

explain standard reason why economic is a science

innocent Reply

factors influencing supply

Petrus Reply

what is economic.

Milan Reply

scares means__________________ends resources. unlimited

Jan

economics is a science that studies human behaviour as a relationship b/w ends and scares means which have alternative uses

Jan

calculate the profit maximizing for demand and supply

Zarshad Reply

Why qualify 28 supplies

Milan

what are explicit costs

Nomsa Reply

out-of-pocket costs for a firm, for example, payments for wages and salaries, rent, or materials

AI-Robot

concepts of supply in microeconomics

David Reply

economic overview notes

Amahle Reply

identify a demand and a supply curve

Salome Reply

i don't know

Parul

there's a difference

Aryan

Demand curve shows that how supply and others conditions affect on demand of a particular thing and what percent demand increase whith increase of supply of goods

Israr

Hi Sir please how do u calculate Cross elastic demand and income elastic demand?

Abari

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Source: OpenStax, Algebra and trigonometry. OpenStax CNX. Nov 14, 2016 Download for free at https://legacy.cnx.org/content/col11758/1.6

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