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The equation of a line can be written in slope-intercept form or standard form. However, when the slope and a point are given, point-slope form is another alternative.

y−y1=m(x−x1)

As its name suggests, point-slope form requires a point on and the slope of the line.

To write the point-slope form for the line that passes through the points$(-1,5)and(1,1),$

find the slope, then use either point to write the equation.
Find the slope

$m=x_{2}−x_{1}y_{2}−y_{1} $

SubstitutePoints

Substitute $(1,1)$ & $(-1,5)$

$m=1−(-1)1−5 $

SubTerm

Subtract term

$m=1−(-1)-4 $

SubNeg

a−(-b)=a+b

$m=2-4 $

CalcQuot

Calculate quotient

m=-2

Choose one point on the line

Substitute values

Write the equation for the line in point-slope form.

Show Solution

To write the equation of the line in point-slope form, y−y1=m(x−x1), we need the slope and a point.
### Example

### The slope

Since we're given the line as a graph we can use the rise and run to find the slope. We'll find the rise and run between two arbitratily chosen points, the y-intercept, (0,-2), and (2,1).
Here, the run is 2 and the rise is 3, which gives a slope of
### Example

### Choosing a point

Next, any point on the line can be used for (x1,y1). Let's use the same point as above, (2,1).
### Example

### Writing the equation

Lastly, substitute the found values of m and (x1,y1) into y−y1=m(x−x1). Here, $m=23 $ and (x1,y1)=(2,1) will be substituted.

All points in the table lie on the same line.

Write the equation of the line in point-slope form.

Show Solution

To write an equation in the form
The equation of the line is y+1=2(x+5).

y−y1=m(x−x1),

the slope of the line, m, and any point on the line, (x1,y1), must be known. We'll begin by finding the slope between consecutive points. It can be seen that the difference between each x-value is 1.
In the right column, we see that the difference between each value is 2.

Therefore, m=2. Next, we need any point on the line. We know that all points in the table are on the line, so we can choose any of them. Let's use (-5,-1) to be (x1,y1.) Substituting this point and m=2 gives us the line.y−y1=m(x−x1)

Substitute

m=2

y−y1=2(x−x1)

SubstituteII

$x_{1}=-5$, $y_{1}=-1$

$y−(-1)=2(x−(-5))$

SubNeg

a−(-b)=a+b

y+1=2(x+5)

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