find r so that the line throiugh (2,6) and (-4,r) is perpendicular to x+2y=1
Put the equation in slope/intercept form.
x + 2y = 1
2y = -x + 1
y = -1/2 x + 1/2
The slope is -1/2; the slope of a line perpendicular to that one is
the negative reciprocal, 2.
The slope is found by dividing the differences of the y co-ordinates
by the differences of the x co-ordinates. Remember, the slope is 2.
(6 - r) / (2 - (-4)) = 2
(6 - r) / (2 + 4) = 2
(6 - r) / 6 = 2
6 - r = 12
-r = 6
r = -6