Chapter 3: Problem 43
Given two points, find the equation of the line. $$ (3,-3),(-5,5) $$
Short Answer
Expert verified
The equation of the line is \(y = -x\).
Step by step solution
01
Identify the Given Points
Identify the coordinates of the two given points: \((x_1, y_1) = (3, -3)\) and \((x_2, y_2) = (-5, 5)\). These will be used to calculate the slope of the line.
02
Calculate the Slope
Use the formula for slope \(m\) to calculate it: \[ m = \frac{y_2 - y_1}{x_2 - x_1} = \frac{5 - (-3)}{-5 - 3} = \frac{8}{-8} = -1. \]The slope \(m\) of the line is \(-1\).
03
Use Point-Slope Form
Use the point-slope form of a line equation, which is \[ y - y_1 = m(x - x_1), \]with \(m = -1\) and one point, say \((3, -3)\). Substitute these values: \[ y - (-3) = -1(x - 3). \]
04
Simplify to Slope-Intercept Form
Simplify the equation to the slope-intercept form \(y = mx + b\):\[ y + 3 = -x + 3 \]\[ y = -x + 3 - 3 \]\[ y = -x. \]
05
Verify by Checking with Second Point
Substitute the coordinates of the second point \((-5, 5)\) into the line equation to verify:\[ 5 = -(-5) \]\[ 5 = 5 \]The equation is satisfied, confirming it is correct.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Slope Formula
The slope of a line tells us how steep the line is and in which direction it goes. To find it from two points, we use the **Slope Formula**. It measures how much the y-value changes between the two points, compared to the change in the x-value. This is given by:
- Formula: \( m = \frac{y_2 - y_1}{x_2 - x_1} \)
- Use: Determine the steepness of the line
- Example: From points (3,-3) and (-5,5), the slope \( m = \frac{5 - (-3)}{-5 - 3} = \frac{8}{-8} = -1 \)
Point-Slope Form
Once we know the slope of a line, we can jump to the **Point-Slope Form** of a line's equation. This form is highly useful when we know a point on the line and the slope. The equation looks like this:
- Formula: \( y - y_1 = m(x - x_1) \)
- Use: Easy to write an equation if slope and one point are known
- Application: Given \( m = -1 \) and point (3,-3), using the formula gives: \( y + 3 = -1(x - 3) \)
Slope-Intercept Form
The most common and easy form of the equation of a straight line is the **Slope-Intercept Form**. This format is preferred because it's clear and shows both the slope and the y-intercept at a glance. It takes this shape:
- Formula: \( y = mx + b \)
- Use: It shows the slope \( m \) and y-intercept \( b \) clearly
- Example: From \( y + 3 = -x + 3 \), simplify to give \( y = -x \)
Two Points Method
When you have two points, figuring out the line that connects them involves the **Two Points Method**. This is a step-by-step approach in which you:
- Identify both points: (3, -3) and (-5, 5)
- Calculate the slope \( m \) using the Slope Formula
- Put the slope and one point into the Point-Slope Form
- Simplify to obtain the Slope-Intercept Form