SOLUTION: How do I use an equation in point slope form (y + 5 = -1/2(x - 4)

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Question 582247: How do I use an equation in point slope form (y + 5 = -1/2(x - 4)

Answer by KMST(5328) About Me  (Show Source):
You can put this solution on YOUR website!
The point slope form of a linear equation is the first form you write, when you only know the slope and the coordinates of a point. After that you may transform it into an equivalent equation in another form, depending on what you need to do with it.
How you use y+%2B+5+=+%28-1%2F2%29%28x+-+4%29 depends on what you want to use it for.
The equation represents a line with slope -1%2F2 that passes through point (4,-5).
You know that much from the equation.
The numbers subtracted from x and y are the coordinates of the point in the point slope form of the equation.
The slope is the number multiplying the x. (The slope is used to find out if the line is parallel or perpendicular to another line).
The point and the slope from the equation can be a good start to graph the line.
There are infinite equations in point slope form for the same line. Each point in the line can be used to get a different (but equivalent) equation.
If a problem asks to write the equation of the line passing through point (-8,1) with slope -1/2, you would first write
y-1=%28-1%2F2%29%28x-%28-8%29%29 --> y-1=%28-1%2F2%29%28x%2B8%29
Then you could transform it:
y-1=%28-1%2F2%29%28x%2B8%29 --> y-1=%28-1%2F2%29x-4 --> y=%28-1%2F2%29x-3
Similarly, for y+%2B+5+=%28-1%2F2%29%28x+-+4%29:
y+%2B+5+=+%28-1%2F2%29%28x+-+4%29 --> y%2B5=%28-1%2F2%29x%2B2 --> y=%28-1%2F2%29x-3
y=%28-1%2F2%29x-3 is in slope intercept form.
You can see from the equation that the y-intercept is -3. The line crosses the y axis (the line x=0) at (point (0,-3).
The beauty of the slope intercept form is that there is only one for each line. Besides, it gives you the direct recipe to calculate y for any x.
y=%28-1%2F2%29x-3 can also be transformed into 2y=-x-6 by multiplying both sides times 2.
You can then add x to both sides to get x%2B2y=-6.
You can transform it into many other equivalent equations, like
x%2B2y%2B6=0 or 5x%2B10y=-30.