Perpendicular distance question help??! have a test tomorrow (1 Viewer)

[fatima96]

Show that the points A(1,-1) and B(-3,5) are on opposite sides of the line 2x-y+8=0?



please and thankyou

 

[fatima96]

pleaaseee help meee

 

[Drongoski]

for A(1,-1)



for B(-3,5)



Therefore A and B are on opposite sides of the line 2x - y + 8 = 0.



Shokran.

 

[fatima96]

really, so do we need to state that the fact they are + & -, is that our proof? Thanks a bunch btw!

 

[Drongoski]

Normally, when determining the perp. distance of a point from a given line, you take the absolute value of the expression, in case it is negative - since distance cannot be negative. But the opposite signs of the 2 points indicate they are on opposite sides of the line. That's all you need to show (just the sign - no need to even evaluate fully the expression) .

 

[fatima96]

no you do, and thanks very much i understand it clearly