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# 2: Equations and Inequalities

• • Contributed by Jay Abramson
• Principal Lecturer (School of Mathematical and Statistical Sciences) at Arizona State University
• Publisher: 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 www.boundless.com/algebra/te...ties-63-10904/

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

Source: Boundless. “Equations and Inequalities.” Boundless Algebra. Boundless, 21 Jul. 2015. Retrieved 22 Dec. 2015 from 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.