Equation of a Straight Line

We will discuss here about the meaning of equation of a straight line.

Let the straight line be PQ which passes through the origin (0, 0) and inclined at 45° with the positive direction of the x-axis. Let the points on the line PQ are (x$_{1}$, y$_{1}$), (x$_{2}$, y$_{2}$), (x$_{3}$, y$_{3}$), etc.,

According to the definition of coordinates $\frac{y_{1}}{x_{1}}$ = tan 45° = $\frac{y_{2}}{x_{2}}$ = $\frac{y_{3}}{x_{3}}$ = etc.,

Therefore, y$_{1}$ = x$_{1}$, y$_{2}$ = x$_{2}$, y$_{3}$ = x$_{3}$, etc.,

Thus, from the above explanation we conclude that for any point (x, y) on the line,

y-coordinate = x-coordinate

i.e., x = y, where (x, y) is any point on the line.

y = x is the equation of the straight line PQ.

Definition of the equation of a straight line:

The equation of a straight line is the common relation between the x-coordinate and y-coordinate of any point on the line.

Note: The coordinates of any point on the straight line satisfy the equation of the line.

Let the equation of a straight line y = 5x - 2. The point (1, 3) lies on the line y = 5x- 2 because (1, 3) satisfy the equation y = 5x – 2. Since by plugging 1 for x and 3 for y in the equation, we get 3 = 5(1) – 2 i.e., ⟹ 3 = 5 – 2 ⟹ 3 = 3, which is true.

But the point (2, 4) does not a lies on the line y = 5x- 2 because (2, 4) does not satisfy the equation y = 5x – 2.

Since by plugging 2 for x and 4 for y in the equation, we get 4 = 5(2) – 2 i.e., ⟹ 4 = 10 – 2 ⟹ 4 = 8, which is not true.

● Equation of a Straight Line

• Inclination of a Line
• Slope of a Line
• Intercepts Made by a Straight Line on Axes
• Slope of the Line Joining Two Points
• Equation of a Straight Line
• Point-slope Form of a Line
• Two-point Form of a Line
• Equally Inclined Lines
• Slope and Y-intercept of a Line
• Condition of Perpendicularity of Two Straight Lines
• Condition of parallelism
• Problems on Condition of Perpendicularity
• Worksheet on Slope and Intercepts
• Worksheet on Slope Intercept Form
• Worksheet on Two-point Form
• Worksheet on Point-slope Form
• Worksheet on Collinearity of 3 Points
• Worksheet on Equation of a Straight Line

10th Grade Math

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