SOLUTION: Find an equation of the lines containing the given points: (-1,1),(5,-5)

Algebra ->  Algebra  -> Test -> SOLUTION: Find an equation of the lines containing the given points: (-1,1),(5,-5)       Log On

Ad: Algebrator™ solves your algebra problems and provides step-by-step explanations!
Ad: Algebra Solved!™: algebra software solves algebra homework problems with step-by-step help!

   


Question 117247: Find an equation of the lines containing the given points:
(-1,1),(5,-5)

Answer by jim_thompson5910(21667) About Me  (Show Source):
You can put this solution on YOUR website!
First lets find the slope through the points (-1,1) and (5,-5)

m=%28y%5B2%5D-y%5B1%5D%29%2F%28x%5B2%5D-x%5B1%5D%29 Start with the slope formula (note: is the first point (-1,1) and is the second point (5,-5))

m=%28-5-1%29%2F%285--1%29 Plug in y%5B2%5D=-5,y%5B1%5D=1,x%5B2%5D=5,x%5B1%5D=-1 (these are the coordinates of given points)

m=+-6%2F6 Subtract the terms in the numerator -5-1 to get -6. Subtract the terms in the denominator 5--1 to get 6


m=-1 Reduce

So the slope is
m=-1

------------------------------------------------


Now let's use the point-slope formula to find the equation of the line:



------Point-Slope Formula------
y-y%5B1%5D=m%28x-x%5B1%5D%29 where m is the slope, and is one of the given points

So lets use the Point-Slope Formula to find the equation of the line

y-1=%28-1%29%28x--1%29 Plug in m=-1, x%5B1%5D=-1, and y%5B1%5D=1 (these values are given)


y-1=%28-1%29%28x%2B1%29 Rewrite x--1 as x%2B1


y-1=-x%2B%28-1%29%281%29 Distribute -1

y-1=-x-1 Multiply -1 and 1 to get -1

y=-x-1%2B1 Add 1 to both sides to isolate y

y=-x%2B0 Combine like terms -1 and 1 to get 0

y=-x Remove the zero terms
------------------------------------------------------------------------------------------------------------
Answer:


So the equation of the line which goes through the points (-1,1) and (5,-5) is: y=-x

The equation is now in y=mx%2Bb form (which is slope-intercept form) where the slope is m=-1 and the y-intercept is b=0

Notice if we graph the equation y=-x and plot the points (-1,1) and (5,-5), we get this: (note: if you need help with graphing, check out this solver)

drawing%28500%2C+500%2C+-7%2C+11%2C+-11%2C+7%2C%0D%0Agraph%28500%2C+500%2C+-7%2C+11%2C+-11%2C+7%2C%28-1%29x%2B0%29%2C%0D%0Acircle%28-1%2C1%2C0.12%29%2C%0D%0Acircle%28-1%2C1%2C0.12%2B0.03%29%2C%0D%0Acircle%285%2C-5%2C0.12%29%2C%0D%0Acircle%285%2C-5%2C0.12%2B0.03%29%0D%0A%29+ Graph of y=-x through the points (-1,1) and (5,-5)

Notice how the two points lie on the line. This graphically verifies our answer.