Chapter 12: Problem 3
Plot the following graphs on the same axes between the values \(x=-3\) to \(x=+3\) and determine the gradient and \(y\)-axis intercept of each. (a) \(y=3 x\) (b) \(y=3 x+7\) (c) \(y=-4 x+4\) (d) \(y=-4 x-5\)
Short Answer
Expert verified
(a) Gradient: 3, Y-intercept: 0; (b) Gradient: 3, Y-intercept: 7; (c) Gradient: -4, Y-intercept: 4; (d) Gradient: -4, Y-intercept: -5.
Step by step solution
01
Understanding Linear Equations
Each equation given is in the form of a straight line, represented by the general equation \(y = mx + c\), where \(m\) is the gradient and \(c\) is the \(y\)-intercept.
02
Finding the Gradient and Y-Intercept
For each equation, identify \(m\) (the coefficient of \(x\)) as the gradient and \(c\) (the constant term) as the \(y\)-intercept. (a) For \(y = 3x\): Gradient \(m = 3\), Y-intercept \(c = 0\). (b) For \(y = 3x + 7\): Gradient \(m = 3\), Y-intercept \(c = 7\). (c) For \(y = -4x + 4\): Gradient \(m = -4\), Y-intercept \(c = 4\). (d) For \(y = -4x - 5\): Gradient \(m = -4\), Y-intercept \(c = -5\).
03
Plotting the Graphs
To plot the graphs, select several values of \(x\) between \(-3\) and \(+3\). Calculate \(y\) for each equation using these \(x\) values and then plot the points on a Cartesian plane. Draw a straight line through the plotted points for each equation.
04
Analyzing Overlapping Graph Features
After plotting, observe each graph's gradient: Lines with positive gradient (\(y = 3x\) and \(y = 3x + 7\)) will rise as \(x\) increases, while those with negative gradient (\(y = -4x + 4\) and \(y = -4x - 5\)) will fall. Compare their \(y\)-intercepts to determine where each line crosses the \(y\)-axis.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Gradient Calculation
The gradient, also known as the slope of a line, indicates how steep a line is on a graph. It is determined by the change in the vertical direction (along the y-axis) divided by the change in the horizontal direction (along the x-axis). In a linear equation of the form \( y = mx + c\), the gradient is represented by the coefficient \(m\).
Here's how you can identify and interpret the gradient in each scenario:
Here's how you can identify and interpret the gradient in each scenario:
- Positive Gradient: A positive \(m\) value means that as you move along the x-axis, the line rises or goes upwards. For example, in the equations \(y = 3x\) and \(y = 3x + 7\), the gradient \(m = 3\) indicates a rising line.
- Negative Gradient: A negative \(m\) value means that the line falls or goes downwards. In \(y = -4x + 4\) and \(y = -4x - 5\), the gradient \(m = -4\) shows a descending line.
Y-Intercept Identification
The y-intercept is the point where the line crosses the y-axis. It occurs when the value of x is zero. In the linear equation \(y = mx + c\), the y-intercept is represented by the constant term \(c\). It tells where the line will intersect the vertical axis of the graph.
For the given equations:
For the given equations:
- In \(y = 3x\), the y-intercept is \(c = 0\), meaning the line crosses the y-axis at the point (0, 0).
- In \(y = 3x + 7\), the y-intercept is \(c = 7\), so the line crosses the y-axis at (0, 7).
- In \(y = -4x + 4\), the y-intercept is \(c = 4\), crossing the y-axis at (0, 4).
- In \(y = -4x - 5\), the y-intercept is \(c = -5\), where the line intersects at (0, -5).
Graph Plotting
Plotting a graph involves drawing the line that corresponds to each equation between defined values, such as \(x = -3\) to \(x = +3\). Here’s a step-by-step guide to effectively plot these lines:
- Choose Points: Select several x-values within the given range. Calculate the corresponding y-values using each equation.
- Plot Points: Write down your calculated (x, y) pairs and plot them on the Cartesian plane.
- Draw the Line: Connect the plotted points with a straight line. Ensure the line is extended and crosses the entire graph region within the given x-range.
Cartesian Plane
The Cartesian plane is a two-dimensional graphing system comprising a horizontal axis (x-axis) and a vertical axis (y-axis). It is named after René Descartes, who developed this coordinate system.
Key features of the Cartesian plane include:
- Origin: The point (0, 0) where the x-axis and y-axis intersect.
- Quadrants: The x and y-axes divide the plane into four quadrants, each representing a unique combination of positive and negative x and y values.
- Horizontal and Vertical Lines: Horizontal lines run parallel to the x-axis, while vertical ones run parallel to the y-axis.