Are the pairs of lines parallel, perpendicular, or intersecting?:

y - 6 = 1/4 (x - 2), y = -4x - 10
2x - y = 7, 3x - 4y = -8
y = - 2/3 x + 7, -2x - 3y = 12

1 answer

To determine whether the pairs of lines are parallel, perpendicular, or intersecting, we first need to convert each equation into the slope-intercept form \( y = mx + b \), where \( m \) represents the slope.

Pair 1:

  1. Equation 1: \( y - 6 = \frac{1}{4}(x - 2) \)

    We can rewrite this in slope-intercept form: \[ y - 6 = \frac{1}{4}x - \frac{1}{2} \] \[ y = \frac{1}{4}x + 5.5 \] Slope \( m_1 = \frac{1}{4} \)

  2. Equation 2: \( y = -4x - 10 \)

    Slope \( m_2 = -4 \)

To check if they are parallel or perpendicular:

  • Two lines are parallel if their slopes are equal: \( m_1 = m_2 \).
  • Two lines are perpendicular if the product of their slopes is \(-1\): \( m_1 \cdot m_2 = -1 \).

Calculating the product: \[ \frac{1}{4} \cdot (-4) = -1 \] Since their slopes satisfy the condition for being perpendicular, these two lines are perpendicular.

Pair 2:

  1. Equation 1: \( 2x - y = 7 \)

    To get the slope-intercept form: \[ -y = -2x + 7 \] \[ y = 2x - 7 \] Slope \( m_1 = 2 \)

  2. Equation 2: \( 3x - 4y = -8 \)

    Rearranging: \[ -4y = -3x - 8 \] \[ y = \frac{3}{4}x + 2 \] Slope \( m_2 = \frac{3}{4} \)

Checking for parallel or perpendicular:

  • Product of slopes: \[ 2 \cdot \frac{3}{4} = \frac{3}{2} \] Since the slopes are not equal and their product is not \(-1\), these lines are intersecting.

Pair 3:

  1. Equation 1: \( y = -\frac{2}{3}x + 7 \)

    Slope \( m_1 = -\frac{2}{3} \)

  2. Equation 2: \( -2x - 3y = 12 \)

    Rearranging: \[ -3y = 2x + 12 \] \[ y = -\frac{2}{3}x - 4 \] Slope \( m_2 = -\frac{2}{3} \)

Checking for parallel or perpendicular:

  • Product of slopes: \[ -\frac{2}{3} \cdot -\frac{2}{3} = \frac{4}{9} \] Since the slopes are equal, these lines are parallel.

Summary:

  1. First pair: Perpendicular
  2. Second pair: Intersecting
  3. Third pair: Parallel