Chapter 1: Problem 36
Find an equation for the line that is described. Write the answer in the two forms \(y=m x+b\) and \(A x+B y+C=0\). Is perpendicular to \(x-y+2=0\) and passes through (3,1).
Short Answer
Expert verified
The equations are \(y = -x + 4\) and \(x + y - 4 = 0\).
Step by step solution
01
Identify the Slope of the Given Line
The equation provided is \(x - y + 2 = 0\). This can be rewritten in the form \(y = mx + b\) to better identify the slope. Rearrange the equation:\[-y = -x - 2\]\[y = x + 2\]Thus, the slope \(m\) of the given line is \(1\).
02
Determine the Perpendicular Slope
A line that is perpendicular to another has a slope that is the negative reciprocal of the original line's slope. The slope of the given line is \(1\). The negative reciprocal is:\[m_{ ext{perpendicular}} = -\frac{1}{1} = -1\]
03
Use Point-Slope Form to Find the Line Equation
We need a line that has a slope of \(-1\) and passes through the point \((3,1)\). Using the point-slope form \(y - y_1 = m(x - x_1)\) where \((x_1, y_1) = (3, 1)\) and \(m = -1\):\[y - 1 = -1(x - 3)\]Simplify the equation:\[y - 1 = -x + 3\]\[y = -x + 4\]
04
Write the Equation in Two Forms
The equation \( y = -x + 4 \) is already in the slope-intercept form \( y = mx + b \). To convert it to the standard form \(Ax + By + C = 0\), rearrange the terms:\[x + y - 4 = 0\]Thus, the equation in standard form is \(x + y - 4 = 0\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Slope-intercept form
The slope-intercept form of an equation of a line is one of the simplest and most common ways to represent lines in algebra. This form is written as \(y = mx + b\). Here, \(m\) represents the slope of the line, while \(b\) is the y-intercept, which is the point where the line crosses the y-axis.
This form makes it very easy to quickly determine both the direction and steepness of a line, which is why it is so popular.
This form makes it very easy to quickly determine both the direction and steepness of a line, which is why it is so popular.
- If \(m > 0\), the line slopes upwards.
- If \(m < 0\), the line slopes downwards.
- If \(m = 0\), the line is horizontal.
Standard form
The equation of a line in standard form is expressed as \(Ax + By + C = 0\). In this form, \(A\), \(B\), and \(C\) are constants, and \(A\) and \(B\) cannot both be zero. This form provides a different perspective than the slope-intercept form by focusing on anchor points in the coordinate plane.
While it may not immediately reveal the slope or y-intercept, converting from standard form to slope-intercept form can make these quantities apparent.
While it may not immediately reveal the slope or y-intercept, converting from standard form to slope-intercept form can make these quantities apparent.
- Rewriting in slope-intercept form helps find the slope \((m = -A/B)\).
- This form is especially useful for solving systems of equations using elimination methods.
- Easy to verify if a particular point \((x, y)\) lies on the line by substituting \(x\) and \(y\) into the equation.
Perpendicular lines
Perpendicular lines intersect at a right angle (90 degrees). A key characteristic of perpendicular lines is their slopes, which relate to each other as negative reciprocals. If a line has a slope \(m\), the slope of a line perpendicular to it is \(-1/m\).
- For example, if one line's slope is \(2\), a perpendicular line's slope would be \(-1/2\).
- This concept is critical for determining orthogonal intersections or geometric figures' attributes.
- In coordinate geometry, this property helps construct squares, rectangles, and right triangles efficiently.
Point-slope form
The point-slope form is useful for writing equations of lines when you have a specific point and the slope. This form is written as \(y - y_1 = m(x - x_1)\), where \((x_1, y_1)\) is a given point on the line and \(m\) is the slope. Point-slope form is particularly handy when working through problems involving coordinates
- This format instantly aligns with given data without requiring the y-intercept.
- By inputting known values, it readily produces an equation of the line.
- It facilitates easy conversion to other forms such as slope-intercept or standard form.