Question

Trying to study for a unit test tomorrow, refresh me on this please!!
Write an equation of the line, in point-slope form, that passes through the two given points.

points: (–2, 15), (9, –18)

Answer 1

Do you know how to compute the slope of the line determined by the two points?

Answer 2

Is it the
m=y1-x1/y2-x2

Answer 3

Almost. See the attached file.
Think of slope as change in y over change in x.
So, m = (y1 - y2) / (x1 - x2) where (x1,y1) and (x2, y2) are points on the line.

Answer 4

So will it look like:
m=(-2-9)/(15-(-18))

Answer 5

So, slope here is m = [(15) - (-18) / [(-2) - (9)].
How does yours differ from mine. I'm not saying mine is for sure correct.

Answer 6

The difference in the y values goes on top. Think of slope as change in y over change in x.

Answer 7

Looks similar just more parenthesis, and organized differently

Answer 8

y-2=-1/3(x+15) is that right?!?!

Answer 9

Your slope = -1/3.
My slope = -3.
You flipped the formula.
It is the difference in the y values divided by the difference in the x values.
You have the difference in the x values divided by the difference in the y values. That is not the correct formula. It is not the correct slope.

Answer 10

Do you see that?

Answer 11

Now, use y - y1 = x - x1 to get the equation of the line.
Let (–2, 15) be (x1, y1).
@kim2012 Question?

Answer 12

I'm waiting to hear from you.

Answer 13

y-2=-3(x-15)

Answer 14

What does that simplify to?
y-2=-3(x-15)
Or, is this point/slope form?
I was thinking slope/intercept form but that is not what was asked.

Answer 15

Im trying to find out the eqaution i would use in order to find those two points. So if the slope it 3 then it think its that or
y-15=-3(x+2)

Answer 16

Now, use y - y1 = x - x1 to get the equation of the line.
Let (–2, 15) be (x1, y1).
============

y - (-15) = -3(x - (-2) )
y + 15 = -3(x + 2)
y + 15 = -3x - 6---->

==========
y-2=-3(x-15)
Do you see where your sign error happened?

Answer 17

Okay, I hear you. There are several ways to write the same equation.
But, you have sign errors to see about and also you need to practice the slope formula.

Answer 18

One nice thing about Algebra is that it is not a guessing game.

So, if you use the formula correctly, you should get the equation:

y - (-15) = -3(x - (-2) )
y + 15 = -3(x + 2)
y + 15 = -3x - 6---->

Answer 19

Show the steps. These negative terms when subtracted can be tricky.