LineI'm not sure if i have enough elements to find the equation of the line . I know slope -2 and a point (-1,1).

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hala718's profile pic

hala718 | High School Teacher | (Level 1) Educator Emeritus

Posted on

To write equation of the line you need the slope and one point on the line.

The equation of the line is given by:

y- y1 = m (x-x1) such that (x,y1) is a point on the line and m is the slope.

Now we can substitute with the given information.

==> y- 1 = -2 ( x + 1)

==> y-1 = -2x -2

==> y= -2x -2 + 1

==> y= -2x - 1

Then the equation of the line is y= -2x -1

pohnpei397's profile pic

pohnpei397 | College Teacher | (Level 3) Distinguished Educator

Posted on

Yes, you have enough.  The slope intercept form of the equation of a line is

y = mx + b

Right now, you have everything but "b."  So all you have to do is plug numbers in and solve for b.

1 = -2(-1) + b

1 = 2 + b

b = -1

So your equation is

y = -2x -1

Wiggin42's profile pic

Wiggin42 | Student, Undergraduate | (Level 2) Valedictorian

Posted on

We know slope is -2 and a point (-1,1). 

Fittingly enough, in this case, its best to write this in point-slope form. 

y - y1 = m(x - x1) where m is a slope and (x1, y1) is a point. 

Plug into that formula: 

y - 1 = -2(x + 1)

If you like, you can distribute the -2 and solve for y to put that in slope-intercept form. But this is also an acceptable answer. 

giorgiana1976's profile pic

giorgiana1976 | College Teacher | (Level 3) Valedictorian

Posted on

Of course,you have!

There are the exactly elements you need to write the equation of the line in the point slope form:

y - y1 = m(x - x1)

We'll identify the coordinate x1 = -1 and y1 = 1 and the slope m = -2.

Now, we'll substitute them in the equation above:

y - 1 = (-2)[x - (-1)]

y - 1 = -2x - 2

We'll add 1 both sides:

The equation of the line is: y = -2x - 1.

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