Chapter 10: Problem 1
Find the equations of the lines that pass through the following points: (a) (1,-1),(2,2) (b) (0,1),(1,-1)
Short Answer
Expert verified
(a) y = 3x - 4; (b) y = -2x + 1
Step by step solution
01
Find the Slope (a)
To find the slope of the line passing through points (1, -1) and (2, 2), use the formula for slope: \( m = \frac{y_2 - y_1}{x_2 - x_1} \) Substituting the coordinates \((x_1, y_1) = (1, -1)\) and \((x_2, y_2) = (2, 2)\), we get: \( m = \frac{2 - (-1)}{2 - 1} = \frac{3}{1} = 3 \)
02
Write the Point-Slope Equation (a)
Using the point-slope form of a line \( y - y_1 = m(x - x_1) \), with slope \( m = 3 \) and point (1, -1), the equation becomes: \( y + 1 = 3(x - 1) \)
03
Convert to Slope-Intercept Form (a)
Simplify the point-slope equation to obtain the line equation in slope-intercept form \(y = mx + b\): \( y + 1 = 3x - 3 \) \( y = 3x - 4 \)
04
Find the Slope (b)
For the line through points (0, 1) and (1, -1), use the slope formula: \( m = \frac{-1 - 1}{1 - 0} = \frac{-2}{1} = -2 \)
05
Write the Point-Slope Equation (b)
With slope \( m = -2 \) and point (0, 1), the point-slope form is: \( y - 1 = -2(x - 0) \)This simplifies directly to: \( y - 1 = -2x \)
06
Convert to Slope-Intercept Form (b)
Rearrange the equation to the form \(y = mx + b\): \( y = -2x + 1 \)
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Slope calculation
Calculating the slope of a line is a fundamental concept in algebra and geometry. It determines how steep a line is and in which direction it moves. To find the slope of a line passing through two points, \( (x_1, y_1) \) and \( (x_2, y_2) \), you use the slope formula: \( m = \frac{y_2 - y_1}{x_2 - x_1} \). This equation essentially measures the change in the vertical direction (rise) over the change in the horizontal direction (run).
- In our example, calculating the slope between the points \( (1, -1) \) and \( (2, 2) \), we substitute the coordinates into the formula, resulting in: \( m = \frac{2 - (-1)}{2 - 1} = \frac{3}{1} = 3 \). This means that for every 1 unit we move to the right, the line rises by 3 units.
- To calculate the slope for points \( (0, 1) \) and \( (1, -1) \), substitute and solve: \( m = \frac{-1 - 1}{1 - 0} = -2 \). This negative slope indicates the line falls 2 units for every 1 unit it moves to the right.
Point-slope form equation
Once the slope is known, forming an equation in the point-slope form is the next step. The point-slope formula is given by \( y - y_1 = m(x - x_1) \). This form is useful because it clearly shows both the slope and a single point that the line passes through.
- For a line with slope \( m = 3 \) passing through \( (1, -1) \), the point-slope equation becomes: \( y + 1 = 3(x - 1) \). This stage ties the line's position to the specific point given, making the equation tangible.
- In another scenario, for a slope of \( m = -2 \) through \( (0, 1) \), the equation simplifies to \( y - 1 = -2(x - 0) \). It shows how easy it is to use point-slope form to establish the trajectory of a line.
Slope-intercept form conversion
The slope-intercept form of a line is popular because it directly shows the line's slope and y-intercept, making it easy to graph. This form is written as \( y = mx + b \).
- To convert the point-slope form \( y + 1 = 3(x - 1) \) into slope-intercept form, distribute and rearrange to obtain: \( y = 3x - 4 \). Here, \( m = 3 \) indicates the steepness of the line, and \( b = -4 \) represents where the line crosses the y-axis.
- For the equation \( y - 1 = -2x \), rearrange to find \( y = -2x + 1 \). Again, \( m = -2 \) describes the downward slope, while \( b = 1 \) is the y-intercept, where the line meets the y-axis.