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Posted by on Thursday, August 26, 2010 at 10:42pm.

Write the equation of the line that passes through the (-2,1) and is perpendicular to y=5.

Okay, I don't understand how I can do this without a slope.

  • Algebra - , Thursday, August 26, 2010 at 11:17pm

    y = 5 or
    y = 0x + 5 , has a slope of zero and is a horizontal line
    so the perpendicular must be a vertical line, but
    you probably have learned that a vertical line has an undefined slope.

    It helps to know that any horizontal line has the form
    y = k, where k is the y value of all the points on the horizontal line (they would all be the same)

    the equation of a vertical line is x = k, were k is the x value of all the points on that vertical line.

    so all we have to do is "look at" the given point,
    and we see that the x value is -2

    so the equation is simply
    x = -2

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