# 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).

### 4 Answers | Add Yours

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**

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

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.

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.**