Chapter 14: Problem 5
Find the equation of a line through (2,-3) that is parallel to the line with equation \(r=3 i-7 j+\lambda(4 i-3 j)\).
Short Answer
Expert verified
The equation of the line is \(y = -\frac{3}{4}x - \frac{3}{2}\).
Step by step solution
01
Understand the Given Line
The given line is expressed in vector form, with equation \( \mathbf{r} = 3\mathbf{i} - 7\mathbf{j} + \lambda(4\mathbf{i} - 3\mathbf{j}) \). This represents a line through the point \((3, -7)\) and in the direction of \((4, -3)\).
02
Identify the Slope of the Given Line
The direction vector of the line is \((4, -3)\). The slope of a line having the direction vector \((a, b)\) is \( \frac{b}{a} \). Therefore, the slope of this line is \(-\frac{3}{4}\).
03
Use the Slope for the Parallel Line
Lines that are parallel have the same slope. Hence, the slope of the line through \((2, -3)\) that is parallel to the given line is also \(-\frac{3}{4}\).
04
Apply the Point-Slope Form
The point-slope form of a line's equation is \(y - y_1 = m(x - x_1)\). Here, \((x_1, y_1) = (2, -3)\) and the slope \(m = -\frac{3}{4}\). Substitute these values to get: \[y + 3 = -\frac{3}{4}(x - 2)\].
05
Simplify to Find the Line's Equation
Expand and simplify the equation: \[y + 3 = -\frac{3}{4}x + \frac{3}{2}\]. Subtract 3 from both sides to get: \[y = -\frac{3}{4}x + \frac{3}{2} - 3\]. Further simplification gives: \[y = -\frac{3}{4}x - \frac{3}{2}\].
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Vector Equations
Vector equations are a way to represent lines in a more geometric form. A vector equation of a line typically includes a starting point vector and a direction vector. For instance, in the problem at hand, the line is given as \( \mathbf{r} = 3\mathbf{i} - 7\mathbf{j} + \lambda(4\mathbf{i} - 3\mathbf{j}) \). This is interpreted as:
- \( 3\mathbf{i} - 7\mathbf{j} \), the point from which the line passes.
- \( \lambda(4\mathbf{i} - 3\mathbf{j}) \), a direction vector scaled by a parameter \( \lambda \).
Slope-Intercept Form
The slope-intercept form is a popular way to express the equation of a line. It is represented as \( y = mx + b \), where \( m \) is the slope and \( b \) is the y-intercept. This form is straightforward because it openly tells us:
Knowing the slope makes understanding the line's behavior intuitive. Negative slopes imply that as \( x \) increases, \( y \) decreases, which visually tilts the line downwards from left to right.
- How steep the line is through its slope \( m \).
- Where the line crosses the y-axis, indicated by \( b \).
Knowing the slope makes understanding the line's behavior intuitive. Negative slopes imply that as \( x \) increases, \( y \) decreases, which visually tilts the line downwards from left to right.
Point-Slope Form
The point-slope form is particularly effective for writing equations of lines when you're given a point and a slope. It is expressed as \( y - y_1 = m(x - x_1) \). Here, \((x_1, y_1)\) is a known point on the line, and \( m \) is the slope. This form is advantageous because:
- It's easy to construct using a specific point and slope.
- It helps transition to other forms, like the slope-intercept form, by simplification.