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2: Equations and Inequalities

• • Contributed by Jay Abramson
• Principal Lecturer (School of Mathematical and Statistical Sciences) at Arizona State University
• Sourced from OpenStax CNX

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An equation states that two expressions are equal, while an inequality relates two different values.

Source: Boundless. “Equations and Inequalities.” Boundless Algebra. Boundless, 21 Jul. 2015. Retrieved 22 Dec. 2015 from https://www.boundless.com/algebra/te...ties-63-10904/

Source: Boundless. “Equations and Inequalities.” Boundless Algebra. Boundless, 21 Jul. 2015. Retrieved 22 Dec. 2015 from https://www.boundless.com/algebra/te...ties-63-10904/
An equation states that two expressions are equal, while an inequality relates two different values.

Source: Boundless. “Equations and Inequalities.” Boundless Algebra. Boundless, 21 Jul. 2015. Retrieved 22 Dec. 2015 from https://www.boundless.com/algebra/te...ties-63-10904/

Source: Boundless. “Equations and Inequalities.” Boundless Algebra. Boundless, 21 Jul. 2015. Retrieved 22 Dec. 2015 from https://www.boundless.com/algebra/te...ties-63-10904/

Recall that a function is a relation that assigns to every element in the domain exactly one element in the range. Linear functions are a specific type of function that can be used to model many real-world applications, such as plant growth over time. In this chapter, we will explore linear functions, their graphs, and how to relate them to data.

• 2.1: Prelude to Equations and Inequalities
The fundamentals of Equations are critical for many aspects of modern life.
• 2.2: The Rectangular Coordinate Systems and Graphs
Descartes introduced the components that comprise the Cartesian coordinate system, a grid system having perpendicular axes. Descartes named the horizontal axis the $$x$$-axis and the vertical axis the $$y$$-axis. This system, also called the rectangular coordinate system, is based on a two-dimensional plane consisting of the $$x$$-axis and the $$y$$-axis. Perpendicular to each other, the axes divide the plane into four sections. Each section is called a quadrant.
• 2.3: Linear Equations in One Variable
A linear equation is an equation of a straight line, written in one variable. The only power of the variable is 1. Linear equations in one variable may take the form ax+b=0ax+b=0 and are solved using basic algebraic operations.
• 2.4: Models and Applications
A linear equation can be used to solve for an unknown in a number problem. Applications can be written as mathematical problems by identifying known quantities and assigning a variable to unknown quantities.  There are many known formulas that can be used to solve applications. Distance problems are solved using the $$d = rt$$ formula. Many geometry problems are solved using the perimeter formula $$P =2L+2W$$, the area formula $$A =LW$$, or the volume formula $$V =LWH$$.
• 2.5: Complex Numbers
The square root of any negative number can be written as a multiple of i. To plot a complex number, we use two number lines, crossed to form the complex plane. The horizontal axis is the real axis, and the vertical axis is the imaginary axis. Complex numbers can be added and subtracted by combining the real parts and combining the imaginary parts. Complex numbers can be multiplied and divided.
• 2.6: Quadratic Equations
Many quadratic equations can be solved by factoring when the equation has a leading coefficient of 1 or if the equation is a difference of squares. The zero-factor property is then used to find solutions. Many quadratic equations with a leading coefficient other than 1 can be solved by factoring using the grouping method. Another method for solving quadratics is the square root property. The variable is squared. We isolate the squared term and take the square root of both sides of the equation.
• 2.7: Other Types of Equations
Rational exponents can be rewritten several ways depending on what is most convenient for the problem. To solve, both sides of the equation are raised to a power that will render the exponent on the variable equal to 1.  Factoring extends to higher-order polynomials when it involves factoring out the GCF or factoring by grouping. We can solve radical equations by isolating the radical and raising both sides of the equation to a power that matches the index.
• 2.8: Linear Inequalities and Absolute Value Inequalities
In this section, we will explore various ways to express different sets of numbers, inequalities, and absolute value inequalities.