# Thread: Find the equation of the line joining (0-3), (-5,0)

1. ## Find the equation of the line joining (0-3), (-5,0)

Question: Find the equation of the line joining $\displaystyle (0-3)$, $\displaystyle (-5,0)$

I encountered a problem when finding the gradient. y2-y1/x2-x1

If $\displaystyle (0, -3)$ is the x1,y1

$\displaystyle 0-(-3)/-5-0$ = $\displaystyle 3/-5$ = $\displaystyle -0.6$

If $\displaystyle (0, -3)$ is the x2,y2

$\displaystyle -3-0/0-5$ = $\displaystyle -3/-5$ = $\displaystyle 0.6$

Where am I wrong? [Solved]

My workings for this question:

$\displaystyle =$ $\displaystyle (-3-0)/(0-(-5)$
$\displaystyle =$ $\displaystyle -3/5$
$\displaystyle =$$\displaystyle -0.6$
$\displaystyle 0=-0.6(-5)+b$
$\displaystyle 0=3+b$
$\displaystyle 0-3=3-3+b$
$\displaystyle -3=b$
Therefore, $\displaystyle y=-0.6x-3$

Is my answer correct?

2. ## Re: Find the equation of the line joining (0-3), (-5,0)

Originally Posted by FailInMaths
Question: Find the equation of the line joining $\displaystyle (0-3)$, $\displaystyle (-5,0)$

I encountered a problem when finding the gradient. y2-y1/x2-x1

If $\displaystyle (0, -3)$ is the x1,y1

$\displaystyle 0-(-3)/-5-0$ = $\displaystyle 3/-5$ = $\displaystyle -0.6$

If $\displaystyle (0, -3)$ is the x2,y2

$\displaystyle -3-0/0-5$ = $\displaystyle -3/-5$ = $\displaystyle 0.6$

Where am I wrong?
Hi FailInMaths,

You just made one small error. It should be:

$\displaystyle \frac{-3-0}{0-(-5)}=\frac{-3}{5}=-0.6$

3. ## Re: Find the equation of the line joining (0-3), (-5,0)

Originally Posted by masters
Hi FailInMaths,

You just made one small error. It should be:

$\displaystyle \frac{-3-0}{0-(-5)}=\frac{-3}{5}=-0.6$
Oh yeah! I will try to solve this problem now

Thanks

4. ## Re: Find the equation of the line joining (0-3), (-5,0)

Can someone check it for me?

Thanks

5. ## Re: Find the equation of the line joining (0-3), (-5,0)

Originally Posted by FailInMaths

Can someone check it for me?

Thanks
Your answer is indeed correct, but you went to lot of trouble to get there.

You found the slope to be -.6

One of your given points was the y-intercept (0, -3).

Simple substitution into y = mx + b would suffice.

$\displaystyle y = -.6x - 3$

6. ## Re: Find the equation of the line joining (0-3), (-5,0)

Oh,yeah thanks for point out that and thanks for checking my answer

7. ## Re: Find the equation of the line joining (0-3), (-5,0)

Originally Posted by FailInMaths
Oh,yeah thanks for point out that and thanks for checking my answer
You're welcome!!