# Tutor.com Linear Equations Session

##### Nov. 24, 2012

Session Transcript - Math - Algebra, 10/1/2012 3:40PM - Tutor.comSession Date: 10/1/2012 3:40PM
Length: 33.5 minute(s)
Subject: Math - Algebra

System Message
[00:00:00] *** Please note: All sessions are recorded for quality control. ***

thomas (Customer)
[00:00:00] Find the equation of a lined graph

Sarah M (Tutor)
[00:00:08] Welcome to Tutor.com ! How can I help you today?

thomas (Customer)
[00:00:23] I do not know where to start

Sarah M (Tutor)
[00:00:34] Can you type your problem or write it on the board please?

thomas (Customer)
[00:01:19] it is a graph showing -4,3 and 4,3

Sarah M (Tutor)
[00:01:45] Ok and you are asked to write the line equation? Are you asked to use a specific form - like slope-intercept or standard form?

thomas (Customer)
[00:01:52] sorry it is -4,3 and 3,4
[00:02:19] standard form

Sarah M (Tutor)
[00:02:46] Ok, great, we can do that. Can you write the standard form equation on the board?

thomas (Customer)
[00:03:58] i think

Sarah M (Tutor)
[00:04:21] That is the equation for finding the slope and we will definitely need that. Let me write the basic form for the line equations and that will show us what we are working toward.

thomas (Customer)
[00:04:50] ok m is slope

Sarah M (Tutor)
[00:06:01] We have 3 basic forms for line equations and they all say the same thing, just in different formats.
[00:06:05] m is slope
[00:06:16] So, let's start by calculating slope and then we'll put our line into the correct format.
[00:06:39] When we have an ordered pair from a graph, the x value is first and the y value is 2nd.
[00:06:48] Can you use our two points to set up the slope equation?

thomas (Customer)
[00:07:29] using the standard form?
[00:07:37] equation?

Sarah M (Tutor)
[00:07:38] We'll start with the slope equation that you provided.

thomas (Customer)
[00:07:46] ok

Sarah M (Tutor)
[00:08:49] This one is tricky with the similar numbers. Just to be sure we are on the same page, I'm going to write out the points like this....
[00:09:54] So y1 is 3. y2 is positive 4. So our numerator will be 3-4, right?

[00:10:21] x1 is -4 and x2 is positive 3.
[00:10:33] Do you have any questions on where those each went?

thomas (Customer)
[00:11:10] I was told to do it kind of backwards
[00:11:39] like the first # of the second pair minus the first # of the first pair
[00:11:53] then the seocon numbers the same way

Sarah M (Tutor)
[00:12:41] We have to be careful to put the y values on top, but either one could be the first number.
[00:13:55] So you can pick either y value to be first, but the y value has to be on top. Does that make sense?

thomas (Customer)
[00:14:27] ok yes it does, then either way will make it positive, correct?

Sarah M (Tutor)
[00:14:44] Right. What do you calculate for the slope, using either fraction?
[00:15:49] Good! I tried to color code that a little.
[00:15:53] So we know m = 1/7.

thomas (Customer)
[00:16:07] yes

Sarah M (Tutor)
[00:16:15] Now we'll use the point-slope form because we know m. We'll reorganize that into standard form.
[00:16:59] The y and x with a subscript will be replaced with one of our points, the other y and x will remain as y and x.
[00:17:28] Can you fill in the values from one of our points? Either will work.

thomas (Customer)
[00:17:39] subscript is the 1? what is that for

Sarah M (Tutor)
[00:17:59] Mainly to show that the x and y have the same subscript and need to be from the same point.
[00:18:36] It looks like you picked the y from one point and the x from the other.

thomas (Customer)
[00:18:47] oh

Sarah M (Tutor)
[00:19:52] Looks good. Do you have any questions on this portion or how to chose x and y?

thomas (Customer)
[00:20:13] no I think I understand it

Sarah M (Tutor)
[00:20:31] Ok, so this is the point-slope form. To get it into standard form we need to distribute the 1/7 and then move terms around.
[00:20:48] Would you like to try distributing the 1/7?

thomas (Customer)
[00:20:51] ok

Sarah M (Tutor)
[00:22:07] Instead of 4 and 1/7, we'll just have 4/7.
[00:22:36] In standard form we don't want fractions - so if we multiply each term by 7 we can get rid of those.
[00:23:17] Now we want this in the form of Ax + By = C. Can you see how to reorganize this to get the form we want?

thomas (Customer)
[00:23:46] ok

Sarah M (Tutor)
[00:24:11] Be sure to let me know if you have questions!

thomas (Customer)
[00:25:21] is that correct

Sarah M (Tutor)
[00:25:38] You are on the right track. I agree with the -x + 7y.
[00:26:01] When you move -21 to the side with the 4 you'd add it. So 21 + 4.

thomas (Customer)
[00:26:02] oh

Sarah M (Tutor)
[00:26:51] Good, so our line equation is -x + 7y = 25
[00:26:57] Do you have any questions on how we figured that out?

thomas (Customer)
[00:27:50] no but i think my problem is going to be remembering the formulas and when to use them.

Sarah M (Tutor)
[00:28:47] Being able to calculate the slope is an important thing to understand and then you have to just memorize the 3 line forms.
[00:29:02] Usually you are told which of the 3 line equations are needed.

thomas (Customer)
[00:29:17] i am
[00:29:26] so first, find the slope,
[00:29:50] then use the point slope, then

Sarah M (Tutor)
[00:30:09] Right, then convert that to standard form.
[00:30:43] If you are using the slope intercept form you can solve for b by putting in one of your points, so you don't need the point-slope form there.
[00:31:46] If you wanted slope-intercept form we'd solve for b and get 25/7.
[00:32:29] I walked through that quickly, but wanted you to see the steps.

thomas (Customer)
[00:32:41] ok

Sarah M (Tutor)
[00:32:46] Can I clarify anything else for you?

thomas (Customer)
[00:33:04] no i think that is it for now

Sarah M (Tutor)
[00:33:13] Thanks for using Tutor.com.Â Please fill out the survey as you leave so we can learn how we can better help you in the future!Â
[00:33:18] Have a good afternoon!

thomas (Customer)
[00:33:24] thanks you too