Question

Line l1 passes through (-2, 5), and (-1, -10)
Line l2 passes through (5,15), and (3,8).

Find the coordinates of the intersection between the lines. Show all of your work.

Answers

  1. The equations of the lines l1 with points (-2, 5), and (-1, -10) and the line l2 with points (5, 15), and (3, 8), gives the coordinate of the intersection between the lines as the point; (-45/37, -250/37)

    Which method can be used to describe the lines to find the intersection point?

    The slope, m1, of line 1 l1 is found as follows;
    • m1 = (5 – (-10))/(-2- (-1)) = -15
    The equation of line l1 in point and slope form is therefore;
    y1 – 5 = -15•(x – (-2))
    Which gives;
    y1 = -15•(x – (-2)) + 5 = -15•x – 25
    • y1 = -15•x – 25
    The slope, m2, of line 2 l2 is found as follows;
    m2 = (15 – 8)/(5 – 3) = 3.5
    Equation of line l2 is therefore;
    y2 – 15 = 3.5•(x – 5)
    Which gives;
    y2 = 3.5•(x – 5) + 15 = 3.5•x – 2.5
    • y2 = 3.5•x – 2.5
    At the intersection point, we have;
    y1 = y2
    Therefore;
    -15•x – 25 = 3.5•x – 2.5
    18.5•x = -22.5
    x = -22.5/18.5 = -45/37
    y2 = 3.5•x – 2.5
    At the intersection point, we have;
    y = y2 = 3.5×(-22.5/18.5) – 2.5 = -250/37
    y = -250/37
    The coordinates of the intersection between the lines is therefore;
    • (-45/37, -250/37)
    Learn more about the equation of a straight line here:
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