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| Equations of a straight line |
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 A straight line is represented by an equation of the first degree in two variables (x and y). Conversely locus of an equation of the first degree in two variables is a straight line. |
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 A straight line is completely determined by its slope (direction) and a point is given through which the line must pass. |
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 Equation of x-axis: If the y-coordinates of each point on the x-axis is zero (0) and if P (x, y) is any point on x-axis, then y=0. |
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 Equation of y-axis: As the x-coordinates of each point on the |
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| y-axis is zero (0) and if P (x, y) is a point on y-axis, then x = 0. |
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 Equation of a line parallel to y-axis: |
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| Let LM be a straight line parallel to y-axis at a distance k from the y-axis. Then, the abscissa (the x-coordinate), x=k. Hence, the equation of the line parallel to y-axis is x = k. |
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 Equation of a line parallel to x-axis: |
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| Let LM be the line parallel to y-axis at a distance l from the x-axis. Then, the y-coordinate (ordinate) of each point on LM is l. Then, y = l is the equation to a line parallel to x-axis. |
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| Remark: |
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| i) If a line is parallel to y-axis is at a distance of k units from the x-axis, then the equation to the line is x = -k. |
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| ii) If a line parallel to x-axis at a distance of l units from the y-axis, then the equation to the line is y = - l. |
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