Question

Which point on the y-axis lies on the line that passes through point C and is perpendicular to line AB?

Answer 1

If we need our line to pass through point C, then we have to use the x and  coordinates of point C in our new equation.  If that line is to be perpendicular to AB, we also need to find the slope of AB and then take its opposite reciprocal.  First things first.  Point C lies at (6, 4) so we will use x = 6 and y = 4 in our equation in a bit.  The coordinates of A are (-2, 4) and the coordinates of B are (2, -8) so the slope between them is $m= \frac{-8-4}{2-(-2)}$ which is -3.  The opposite reciprocal of -3 is 1/3.  That's the slope we will use along with the points from C to write the new equation.  We will do this by plugging in x, y, and m (slope) into the slope-intercept form of a line and solve for b.  $4= \frac{1}{3} (6)+b$ and 4 = 2 + b.  So b = 2.  That's the y-intercept, the point on the y axis where the line goes through when x is 0.  Therefore, the point you're looking for is (0, 2).