Hi everyone,

I would to check with someone if I didn't make a mistake with the problem below

Positions are given with reference to a Cartesian coordinate system whose x- and y-axes point due East and due North, respectively. Distance is measured in kilometres. An aeroplane flies in a straight line from city A, at (300,-200), to city B, at (-100,600).
((i) Find the equation of the line of flight of the aeroplane.

A(300,-200) B(-100,600)

First find the slope

Run is: -100-300 = -400

Rise is: 600-(-200) = 800

The slope is

M = rise/run = 800/-400 = -2

Mr F says: Correct.
We can apply equation y-y1 = m(x-x1) with m= -2 and either (x1,y1) = (300,-200) or (x1,y1)= (-100,600).

Mr F says: Correct.
First possibility:

y(-200)= -2(x-1)

Mr F says: Wrong! How on Earth did you get it? y - (-200) = -2 (x - 300) => y = .....
y= -2x+202

Thanks again for helping me