The line joining `(4, 2)` and `(3, -5)` has slope `m=(-7)/(-1)=7.`

graph line and its perpendicular

We need to find the equation of the red line.

The line perpendicular to the green dotted line has slope `-1/7.`

The line through `(4, 2)` with slope `-1/7` has equation:

`y-2=-1/7(x-4)`

`=-x/7+4/7`

`y=-x/7+2 4/7`

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