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C1 Coordinate geometry help!

So i'm doing this question andned t give the final answer in the form ax+by+c=0.

I have to find the equation of the line joining the pair of points (-4,2) and (-1,-3).

I calcualte the gradient and get it to be -5/3, and then i use the formual y-y1=M(x-x1) to get Y-3= - 5/3(x-(-4)). But then i get stuck and i keep ending up with the wrong asnwer.

the answer should be 5x +3y +14=0.

Any help would be apprecited thanks
Reply 1
Avatar for lovmaths
lovmaths
1
hazbaz
So i'm doing this question andned t give the final answer in the form ax+by+c=0.

I have to find the equation of the line joining the pair of points (-4,2) and (-1,-3).

I calcualte the gradient and get it to be -5/3, and then i use the formual y-y1=M(x-x1) to get Y-3= - 5/3(x-(-4)). But then i get stuck and i keep ending up with the wrong asnwer.

the answer should be 5x +3y +14=0.

Any help would be apprecited thanks

"i use the formual y-y1=M(x-x1) to get Y-3= - 5/3(x-(-4))"
This bit is where you went wrong.
It should be either
y-2 = -5/3 (x-(-4))
or
y-(-3) = -5/3 (x-(-1))

:smile:
Reply 2
Avatar for ztibor
ztibor
10
hazbaz
So i'm doing this question andned t give the final answer in the form ax+by+c=0.

I have to find the equation of the line joining the pair of points (-4,2) and (-1,-3).

I calcualte the gradient and get it to be -5/3, and then i use the formual y-y1=M(x-x1) to get Y-3= - 5/3(x-(-4)). But then i get stuck and i keep ending up with the wrong asnwer.

the answer should be 5x +3y +14=0.

Any help would be apprecited thanks


You are right up to y-y1=M(x-x1)
You have two options for (x1,y1): (-4,2) and (-1,-3)
So how will be from these Y-3 and x-(-4)). THe given point would be (x1,y1)=(4,3)
Try substituting (-1,-3): y+3=-5/3(x+1)
Reply 3
Avatar for hazbaz
hazbaz
OP
11
ztibor
You are right up to y-y1=M(x-x1)
You have two options for (x1,y1): (-4,2) and (-1,-3)
So how will be from these Y-3 and x-(-4)). THe given point would be (x1,y1)=(4,3)
Try substituting (-1,-3): y+3=-5/3(x+1)


I worked it out thanks just a stupid mistake on my behalve :P
Reply 4
Avatar for DPLSK
DPLSK
14
hazbaz
Find the equation of the line passing through the points (−4,2)(-4, 2) and (−1,−3)(-1, -3).


I will show you the general case and then a very similar question and its solution.

Find the equation of the line passing through two points.

It is paramount that you understand this idea.

Find the equation of the line passing through the points (-5,6) and (-2,-3).

I hope this helps.

Darren
(edited 12 years ago)
Reply 5
Avatar for soup
soup
11
they use that so they don't have to work out c as it all comes out
Reply 6
Avatar for hazbaz
hazbaz
OP
11
Ye i misttok the -y1 to mean the bottom part of teh graident dont ask me why lol. Once i relaised it was the y coordinate it became easy :smile:

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