SOLUTION: How would you solve the problem in point-slope form? A line through (-1,1) and (2,3)

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Question 102884: How would you solve the problem in point-slope form?
A line through (-1,1) and (2,3)

Answer by jim_thompson5910(21685) About Me  (Show Source):
You can put this solution on YOUR website!
First lets find the slope through the points (-1,1) and (2,3)

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 (2,3))

m=%283-1%29%2F%282--1%29 Plug in y%5B2%5D=3,y%5B1%5D=1,x%5B2%5D=2,x%5B1%5D=-1 (these are the coordinates of given points)

m=+2%2F3 Subtract the terms in the numerator 3-1 to get 2. Subtract the terms in the denominator 2--1 to get 3

So the slope is
m=2%2F3

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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=%282%2F3%29%28x--1%29 Plug in m=2%2F3, x%5B1%5D=-1, and y%5B1%5D=1 (these values are given)


y-1=%282%2F3%29%28x%2B1%29 Rewrite x--1 as x%2B1


y-1=%282%2F3%29x%2B%282%2F3%29%281%29 Distribute 2%2F3

y-1=%282%2F3%29x%2B2%2F3 Multiply 2%2F3 and 1 to get 2%2F3

y=%282%2F3%29x%2B2%2F3%2B1 Add 1 to both sides to isolate y

y=%282%2F3%29x%2B5%2F3 Combine like terms 2%2F3 and 1 to get 5%2F3 (note: if you need help with combining fractions, check out this solver)


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Answer:


So the equation of the line which goes through the points (-1,1) and (2,3) is:y=%282%2F3%29x%2B5%2F3

The equation is now in y=mx%2Bb form (which is slope-intercept form) where the slope is m=2%2F3 and the y-intercept is b=5%2F3

Notice if we graph the equation y=%282%2F3%29x%2B5%2F3 and plot the points (-1,1) and (2,3), we get this: (note: if you need help with graphing, check out this solver)

drawing%28500%2C+500%2C+-8.5%2C+9.5%2C+-7%2C+11%2C%0D%0Agraph%28500%2C+500%2C+-8.5%2C+9.5%2C+-7%2C+11%2C%282%2F3%29x%2B5%2F3%29%2C%0D%0Acircle%28-1%2C1%2C0.12%29%2C%0D%0Acircle%28-1%2C1%2C0.12%2B0.03%29%2C%0D%0Acircle%282%2C3%2C0.12%29%2C%0D%0Acircle%282%2C3%2C0.12%2B0.03%29%0D%0A%29+ Graph of y=%282%2F3%29x%2B5%2F3 through the points (-1,1) and (2,3)

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