Find the equation of the line through the point (6 , -1) and is perpendicular to the y axis.
The line is perpendicular to the y-axis means that it is horizontal...
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Let's put the problem in this way: if the line is perpendicular to y-axis, then it is parallel to x-axis.
The slopes of 2 parallel lines are equal:
But the slope of the x-axis is m1=0, so m2=0, also.
Now, let's write the equation of a line which passes through a given point A(6 , -1) and it has a known slope, m2=0:
y - yA = m2(x - xA)
y - (-1) = 0*(x - 6)
y + 1 = 0
y = -1
The equation of the line which is perpendicular to y-axis is:
y = -1