Posted by Sal on .
You are given the cordinates of the four points
A (6,2), B(2.4), C (6, 2) and D (2,4).
Show that the equation of the line DA is 4y3x = 10
help please!!

Geometry 
Reiny,
sub in the points A(6,2) and D(2,4)
into 4y  3x = 10
for (6,2)
LS = 4(2)  3(6) = 10 = RS
for (2,4)
LS = 4(4)  3(2) = 10 = RS
YES , the equation of DA is 4y3x = 10
Where do the other two points enter the picture ? 
Geometry 
Sal,
Could you please explain that in full, as im really struggling to understand. The other two points were for calculating gradients AB, CB, DC and DA but i got that.
Thanks reiny! 
Geometry 
Sal,
Is there a way of simplifying the equation 4y3x=10 to y=0.75x  2.5, then proving that is the equation for DA?

Geometry 
Reiny,
I don't know how much further I can explain it.
Since both points satisfy the given equation, the equation must be the correct one
All I did was replace the x and y in the equation with the x and y of each of the points
LS stands for left side of the equation
RS stands for the right side.
in
4y  3x = 10
4y = 3x  10
y = (3/4)x  10/4
or
y = .75x  2.5
The last equation and the starting equation are really the same thing.
Subbing in either one gives you the same result
e.g.
sub in (6,2) into y = .75x  2.5
LS = 2
RS = .75(6)  2.5 = 4.5  2.5 = 2
since LS = RS , the point lies on the equation.
I will let you sub in the second point in the same way.
Let me know if you did NOT get it. 
Geometry 
Sal,
What is RS and LS?

Geometry 
Reiny,
Did you not read my reply ? I explained what they are.

Geometry 
Sal,
Im sorry!!! Its so late and im half asleep. Worse time to do maths. I get it reiny!!!!!!!
Thank you
So the second point is 4 = 4
therefore it must be the correct equation as both points satisfy the equation? 
Geometry 
Reiny,
You got it.

Geometry 
Sal,
Your a star!!!!!!!!!!!!!
Many thanks