Chapter 37: Problem 658
Find the equation of the straight line passing through the point \((4,-1)\) and having an angle of inclination of \(135^{\circ}\).
Short Answer
Expert verified
The equation of the straight line passing through the point \((4, -1)\) and having an angle of inclination of \(135^{\circ}\) is \(y = -x + 3\).
Step by step solution
01
Find the slope of the line
Given the angle of inclination, we can find the slope of the line using the tangent function:
\[m = \tan(\theta)\]
where \(m\) is the slope, and \(\theta\) is the angle of inclination.
Our angle of inclination is \(135^{\circ}\), so we need to find the tangent of \(135^{\circ}\).
\[m = \tan(135^{\circ})\]
Since \(\tan(135^{\circ}) = -1\), the slope of the line is \(-1\).
02
Use the point-slope formula to find the equation of the line
Now that we have the slope and a point on the line \((4, -1)\), we can use the point-slope form of the equation of a line:
\[y - y_1 = m(x - x_1)\]
Substituting our values for \(m\), \(x_1\), and \(y_1\), we get:
\[y - (-1) = -1(x - 4)\]
03
Simplify the equation
Now we just need to simplify the equation by distributing the slope and combining like terms:
\[y + 1 = -x + 4\]
Subtract \(1\) from both sides:
\[y = -x + 3\]
04
Write the final equation
Finally, write down the equation in its simplified form:
\[y = -x + 3\]
This is the equation of the straight line passing through the point \((4, -1)\) and having an angle of inclination of \(135^{\circ}\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Slope of a Line
To find the slope of a line, you can use the concept of the angle of inclination. The slope, often represented by the letter \(m\), tells us how steep a line is. It is calculated as the ratio of the rise (vertical change) to the run (horizontal change) between two points on the line.
- An upward slope from left to right is positive.
- A downward slope from left to right is negative.
- A horizontal line has no vertical change, so its slope is zero.
- A vertical line has no horizontal change, resulting in an undefined slope.
Point-Slope Formula
The point-slope formula is a mathematical equation used to find the equation of a line when you know the slope and a point through which the line passes. The formula is given by:\[y - y_1 = m(x - x_1) \]Where:
- \(y\) and \(x\) are the variables that represent any point on the line.
- \(y_1\) and \(x_1\) are the coordinates of the given point on the line.
- \(m\) is the slope of the line.
Angle of Inclination
The angle of inclination of a line refers to the angle formed between the line and the positive direction of the x-axis. It's a way of describing how tilted a line is relative to a horizontal line.
- The angle of inclination is measured in degrees (°) or radians.
- Angles between 0° and 90° indicate a line that rises as it moves from left to right.
- An angle of 90° corresponds to a vertical line.
- Angles between 90° and 180° indicate a line that declines as it moves from left to right, like our example of \(135^{\circ}\).
Tangent Function
The tangent function, denoted as \(\tan(\theta)\), is a trigonometric function that can help find the slope of a line through the angle of inclination. It relates the angle in right triangle trigonometry to the ratio of the opposite side to the adjacent side.
- For angles in a unit circle, \(\tan(\theta)\) provides the slope of a line inclined at an angle \(\theta\) to the positive x-axis.
- \(\tan(0^{\circ}) = 0\), meaning a horizontal line.
- For a line inclined at \(135^{\circ}\), \(\tan(135^{\circ}) = -1\), revealing the line's slope in this example.