The Straight Line

The following examples and case studies demonstrate how to apply the various formulas and concepts related to straight lines, including standard forms, families of lines, and calculating distances and angles.

Standard Forms of Equations

Example

Problem 1 (Point-Slope Form): Find the equation of the line passing through the point P(2,5)P(-2, 5) with a slope of 33. Write the final equation in standard general form (Ax+By+C=0Ax + By + C = 0).

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Example

Problem 2 (Slope-Intercept Form): A line has a y-intercept of 4-4 and a slope of 12-\frac{1}{2}. Find its equation in general form.

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Example

Problem 3 (Two-Point Form): Determine the equation of the line passing through A(3,1)A(3, -1) and B(6,5)B(6, 5).

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Example

Problem 4 (Intercept Form): A line has an x-intercept of 55 and a y-intercept of 33. What is its equation?

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Normal Form

Example

Problem 1: The perpendicular distance from the origin to a line is 44 units, and the angle this perpendicular makes with the positive x-axis is 6060^\circ. Find the equation of the line.

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Example

Problem 2: Convert the general equation 3x4y+10=03x - 4y + 10 = 0 into normal form and find the distance to the origin.

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Example

Problem 3: Write the equation x+y6=0x + y - 6 = 0 in normal form. What is the angle of the normal?

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Family of Lines

Example

Case Study 1: Analyze the family of lines given by the equation (2k+1)x+(k3)y+(54k)=0(2k+1)x + (k-3)y + (5-4k) = 0. Prove that all lines in this family pass through a single fixed point, regardless of the value of kk, and find that point.

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Example

Case Study 2: A civil engineer is designing a series of perfectly parallel drainage pipes. The master blueprint line is given by 3x4y+12=03x - 4y + 12 = 0. Express the mathematical family representing all possible parallel pipes, and determine the specific pipe equation that passes exactly through the survey point (5,2)(5, -2).

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Parallel and Perpendicular Lines

Example

Problem 1: Find the equation of a line passing through (4,1)(4, 1) that is parallel to the line 2x5y=102x - 5y = 10.

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Example

Problem 2: Determine the equation of the line passing through (3,2)(-3, 2) that is strictly perpendicular to x+3y+6=0x + 3y + 6 = 0.

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Example

Problem 3: Are the lines 4x6y=94x - 6y = 9 and 3x+2y=53x + 2y = 5 parallel, perpendicular, or neither?

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Distance from a Point to a Line

Example

Problem 1: Calculate the precise perpendicular distance from the point (3,2)(3, -2) to the line 5x12y+4=05x - 12y + 4 = 0.

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Example

Problem 2: Find the altitude of a triangle drawn from vertex A(1,4)A(-1, 4) to the side formed by the line passing through B(2,3)B(2, -3) and C(5,1)C(5, 1).

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Distance Between Parallel Lines

Example

Problem 1: Calculate the exact distance separating the two parallel lines 3x+4y10=03x + 4y - 10 = 0 and 3x+4y+5=03x + 4y + 5 = 0.

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Example

Problem 2: Find the separation distance between the parallel lines 8x6y+7=08x - 6y + 7 = 0 and 4x3y2=04x - 3y - 2 = 0.

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Angle Between Two Lines

Example

Problem 1: Find the acute angle between the intersecting lines 2xy+5=02x - y + 5 = 0 and 3x+y4=03x + y - 4 = 0.

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Example

Problem 2: What is the angle between the lines y=12x+3y = \frac{1}{2}x + 3 and y=3x1y = 3x - 1?

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