SOLVED Find the equation of the line joining (0-3), (-5,0)

Jan 2011
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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:

Gradient = y2-y1/x2-x1
\(\displaystyle =\) \(\displaystyle (-3-0)/(0-(-5)\)
\(\displaystyle =\) \(\displaystyle -3/5\)
\(\displaystyle =\)\(\displaystyle -0.6\)
\(\displaystyle 0=-0.6(-5)+b\)
\(\displaystyle 0=3+b\)
\(\displaystyle 0-3=3-3+b\)
\(\displaystyle -3=b\)
Therefore, \(\displaystyle y=-0.6x-3\)

Is my answer correct?
 
Last edited:

masters

MHF Helper
Jan 2008
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Big Stone Gap, Virginia
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:

\(\displaystyle \frac{-3-0}{0-(-5)}=\frac{-3}{5}=-0.6\)
 
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Jan 2011
104
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Added my answer for the question

Can someone check it for me?

Thanks
 

masters

MHF Helper
Jan 2008
2,550
1,187
Big Stone Gap, Virginia
Added my answer for the question

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.

\(\displaystyle y = -.6x - 3\)
 
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Jan 2011
104
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Oh,yeah thanks for point out that and thanks for checking my answer