Answer
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Hint: Express the equation of$x$- axis in the form$Ax + By + C = 0$ and find its slope using the formula $m = \dfrac{{ - A}}{B}$ where m represents the slope.
Use the fact that parallel lines have the same slope to calculate the slope of the line parallel to the $x$- axis. Use this slope and the general equation of the parallel line $Ax + By + {C_1} = 0$ where $C \ne {C_1}$ to get the answer.
Complete step by step answer:
We are asked to find the equation of a straight line which is parallel to the $x$- axis.
We know that the equation of the $x$- axis is$y = 0$
This means that any point on the $x$- axis will have its $y - $ coordinate as 0.
Any line which is parallel to the $x$- axis will look like the below figure:
That is, the line will lie either above the $x$- axis or below it. Also, it will pass through the $y$- axis.
The general equation of a straight line is given by $Ax + By + C = 0$
Here, the letters A, B, and C are real numbers. Also, A and B are non-zero constants.
Now, the slope of the straight line given by the equation $Ax + By + C = 0$is $m = \dfrac{{ - A}}{B}$ where $B \ne 0$
We will compare the equation of $x$- axis with the general form $Ax + By + C = 0$to obtain its slope.
Now, the equation of $x$- axis is $y = 0$.
Therefore, we can express this equation as $0x + y + 0 = 0$.
Thus on comparison with the general form $Ax + By + C = 0$, we get $A = 0$,$B = 1$ and $C = 0$
Therefore, the slope of the equation of $x$- axis is $m = - \dfrac{0}{1} = 0$
But the question is not about finding the slope or equation of the $x$- axis.
We need the equation of the line parallel to the $x$- axis.
Now, we know that the general equation of any line which is parallel to the line represented by the equation $Ax + By + C = 0$ would be of the form $Ax + By + {C_1} = 0$ where $C \ne {C_1}$ and ${C_1}$ is also a real number.
We can notice here that the coefficients A and B of the variables $x$ and $y$ are the same for a pair of parallel lines.
Therefore, the slope of a line parallel to the line represented by the equation $Ax + By + C = 0$will also be given by $m = \dfrac{{ - A}}{B}$ where $B \ne 0$
Thus, we can conclude that parallel lines have the same slope.
Therefore, the slope of the line parallel to the $x$- axis will be 0 as well.
This is only possible if $A = 0$as$m = \dfrac{{ - A}}{B} = 0 \Rightarrow - A = 0 \Rightarrow A = 0$
Substitute$A = 0$ in the general equation of the parallel line $Ax + By + {C_1} = 0$
This gives us
$
0x + By + {C_1} = 0 \\
\Rightarrow By = - {C_1} \\
\Rightarrow y = \dfrac{B}{{ - {C_1}}} = - \dfrac{B}{{{C_1}}} \\
$
Let$ - \dfrac{B}{{{C_1}}} = a$.
Thus the equation becomes $y = a$
Hence the equation of any line parallel to $x$- axis is $y = a$
Note:
A common mistake made by many students is that they tend to take the coefficient of $x$ in the numerator and that of $y$ in the denominator to calculate the slope. One needs to be careful with this substitution which is the key to answering such questions.
Use the fact that parallel lines have the same slope to calculate the slope of the line parallel to the $x$- axis. Use this slope and the general equation of the parallel line $Ax + By + {C_1} = 0$ where $C \ne {C_1}$ to get the answer.
Complete step by step answer:
We are asked to find the equation of a straight line which is parallel to the $x$- axis.
We know that the equation of the $x$- axis is$y = 0$
This means that any point on the $x$- axis will have its $y - $ coordinate as 0.
Any line which is parallel to the $x$- axis will look like the below figure:
![seo images](https://www.vedantu.com/question-sets/680f01fa-0c14-439a-ae7b-fc8d205aa8844580967009129207847.png)
That is, the line will lie either above the $x$- axis or below it. Also, it will pass through the $y$- axis.
The general equation of a straight line is given by $Ax + By + C = 0$
Here, the letters A, B, and C are real numbers. Also, A and B are non-zero constants.
Now, the slope of the straight line given by the equation $Ax + By + C = 0$is $m = \dfrac{{ - A}}{B}$ where $B \ne 0$
We will compare the equation of $x$- axis with the general form $Ax + By + C = 0$to obtain its slope.
Now, the equation of $x$- axis is $y = 0$.
Therefore, we can express this equation as $0x + y + 0 = 0$.
Thus on comparison with the general form $Ax + By + C = 0$, we get $A = 0$,$B = 1$ and $C = 0$
Therefore, the slope of the equation of $x$- axis is $m = - \dfrac{0}{1} = 0$
But the question is not about finding the slope or equation of the $x$- axis.
We need the equation of the line parallel to the $x$- axis.
Now, we know that the general equation of any line which is parallel to the line represented by the equation $Ax + By + C = 0$ would be of the form $Ax + By + {C_1} = 0$ where $C \ne {C_1}$ and ${C_1}$ is also a real number.
We can notice here that the coefficients A and B of the variables $x$ and $y$ are the same for a pair of parallel lines.
Therefore, the slope of a line parallel to the line represented by the equation $Ax + By + C = 0$will also be given by $m = \dfrac{{ - A}}{B}$ where $B \ne 0$
Thus, we can conclude that parallel lines have the same slope.
Therefore, the slope of the line parallel to the $x$- axis will be 0 as well.
This is only possible if $A = 0$as$m = \dfrac{{ - A}}{B} = 0 \Rightarrow - A = 0 \Rightarrow A = 0$
Substitute$A = 0$ in the general equation of the parallel line $Ax + By + {C_1} = 0$
This gives us
$
0x + By + {C_1} = 0 \\
\Rightarrow By = - {C_1} \\
\Rightarrow y = \dfrac{B}{{ - {C_1}}} = - \dfrac{B}{{{C_1}}} \\
$
Let$ - \dfrac{B}{{{C_1}}} = a$.
Thus the equation becomes $y = a$
Hence the equation of any line parallel to $x$- axis is $y = a$
Note:
A common mistake made by many students is that they tend to take the coefficient of $x$ in the numerator and that of $y$ in the denominator to calculate the slope. One needs to be careful with this substitution which is the key to answering such questions.
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