Asked by Sal

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 4y-3x = -10

help please!!
Answered by 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 4y-3x = -10

Where do the other two points enter the picture ?
Answered by 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!
Answered by Sal
Is there a way of simplifying the equation 4y-3x=-10 to y=0.75x - 2.5, then proving that is the equation for DA?
Answered by 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.
Answered by Sal
What is RS and LS?
Answered by Reiny
Did you not read my reply ? I explained what they are.
Answered by 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?
Answered by Reiny
You got it.
Answered by Sal
Your a star!!!!!!!!!!!!!
Many thanks
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