SOLUTION: What is the equation of the line passing through the two points (-20,9) and (-15,4)?

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Question 623252: What is the equation of the line passing through the two points (-20,9) and (-15,4)?
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!

First let's find the slope of the line through the points and


Note: is the first point . So this means that x%5B1%5D=-20 and y%5B1%5D=9.
Also, is the second point . So this means that x%5B2%5D=-15 and y%5B2%5D=4.


m=%28y%5B2%5D-y%5B1%5D%29%2F%28x%5B2%5D-x%5B1%5D%29 Start with the slope formula.


m=%284-9%29%2F%28-15--20%29 Plug in y%5B2%5D=4, y%5B1%5D=9, x%5B2%5D=-15, and x%5B1%5D=-20


m=%28-5%29%2F%28-15--20%29 Subtract 9 from 4 to get -5


m=%28-5%29%2F%285%29 Subtract -20 from -15 to get 5


m=-1 Reduce


So the slope of the line that goes through the points and is m=-1


Now let's use the point slope formula:


y-y%5B1%5D=m%28x-x%5B1%5D%29 Start with the point slope formula


y-9=-1%28x--20%29 Plug in m=-1, x%5B1%5D=-20, and y%5B1%5D=9


y-9=-1%28x%2B20%29 Rewrite x--20 as x%2B20


y-9=-1x%2B-1%2820%29 Distribute


y-9=-1x-20 Multiply


y=-1x-20%2B9 Add 9 to both sides.


y=-1x-11 Combine like terms.


y=-x-11 Simplify


So the equation that goes through the points and is y=-x-11