Follow-up on my last post

SlowlyFading · 2012-06-19 03:21:02

Okay, so I understood what i was told in the last post that I posted, so I sent that work to my teacher.
For #2 and #5, I had been given the slope intercept form but I actually need point-slope form. So if somebody could get the answer to #2 and #5 and explain to me how they did it I would greatly appreciate it. Then on #12, she just simple said it was wrong and needs revision. I'm lost on that one and don't understand it..

2. Slope equals 2 and the line goes through the point (-1, 3)

(I need point-slope form)

5. The line goes through the points (1/2, 3/2) and (-1/4, 5/4)

(I need point-slope form)

12. Find the slope-intercept form of the equation that goes through these two points.

(The two points are 1,115.00 and 2,83.00.)

bobbym · 2012-06-19 03:35:25

Hi;

For 12)The slope intercept form is y = mx+b.

I am reading your points as (1,115) and (2,83) am I correct?

m = -32 and b = 147

The equation is

or in point slope form

Which can verified just by plugging in. Did you present it to her correctly?

For 2) the point slope form is

For 5) Use the two points to get the slope:

Now use the point slope form.

Use the first point and plug in.

SlowlyFading · 2012-06-25 16:33:20

The points are actually 1,115.00 and 5,83.00.

So I need to know the slope-intercept form of the equation that goes through these two points and how you got it!

And the point-slope form of the equation that goes through these two points and how you got it!

Sorry about that!

Also, what would the points be for y - 7 = 3(x + 2) and y - 2 = 3(x - 2) ? I don't understand how to do that because I don't know when I'm supposed to change the positive/negative signs.

Bob · 2012-06-25 19:08:17

hi SlowlyFading

bobbym's post 2 shows you what to do.

Go back to his method but put in the correct x coordinate of 5 not 2 and you should get the right equation this time.

For y - 7 = 3(x + 2) I've made a diagram that I hope will help.

You can see the gradient is 3.

So there is a point (-2,7) that taken together with any general point (x,y) must give that gradient.

How did I get (-2,7)? Read on.

Do you see what I've had to do with the signs here?

The method requires

Now the 'y' bit already has a minus with y - 7, so that tells me that the point must have (...,7) as its y coord.

But the x bit has a plus sign with x + 2, so I make it into a double minus (x - - 2) and that tells me the x coord is (-2,...)

That's where (-2,7) came from.

I've used (-1,10) to mark as (x,y). There's no special significance in choosing that point. I could have had any other point; I just chose that because I didn't want the diagram to get too big.

So, to make my diagram, I worked out (-2,7) as I have just shown. Then I counted across 1 and up 3 and marked another point. Then across 1 and up 3 again and so on.

To check I was showing the right line I did this check:

I looked at another coordinate on my line. I chose (0,13) but any point would have done.

I substituted into your original equation to check the numbers worked out:

(13 - 7) = 3 (0 + 2) ......... yes, 6 = 6 so that has worked.

For you other equation

y - 2 = 3(x - 2)

I can see the gradient is 3 again.

Both signs are minus so a point on the line must be (2,2)

Bob

SlowlyFading · 2012-06-26 08:02:11

I don't understand what BobbyM did to get the slope intercept form. I tried doing what he did with my correct points but I just don't get it. I need the slope intercept form to get the point-slope form..

SlowlyFading · 2012-06-26 08:09:53

Oh and Thanks Bob Bundy, I understand how to find the points now! It's way easier then I thought it was, I had thought it was something much more complicated.

bobbym · 2012-06-26 16:49:43

Hi SlowlyFading;

I don't understand what BobbyM did to get the slope intercept form. I tried doing what he did with my correct points but I just don't get it.

Which question are we talking about? Please mention those things, that way answers are quicker.

Bob · 2012-06-26 18:42:49

hi bobbym,

How are you today?

It's his original post, Q12, which you did in post 2 and then he corrected the coordinates in post 3.

I think it appeared in his other thread and he said he hadn't got the right answer.

Bob

bobbym · 2012-06-26 18:59:24

Hi Bob;

It is too hot and my brain is baked.

Hi SlowlyFading;
There are many ways to do this. The prettiest is to use a set of simultaneous equations.

When you solve for m and b you get,

so the equation is

Or, first you get the slope ( you should know how ) then you plug in one point into the point slope form

are you okay up to here? This is the place to speak your mind and let me know what you know.

SlowlyFading · 2012-06-27 02:00:15

So, the point slope form is y - 123 = 8(x - 0) then?

bobbym · 2012-06-27 02:01:39

What point did you pick?

SlowlyFading · 2012-06-27 02:12:49

0

bobbym · 2012-06-27 02:14:19

That is not a point. A point has two numbers (x,y). (0,0) is a point it is the origin.

But you must pick one of the points in the question.

SlowlyFading · 2012-06-27 02:16:13

This is what I did

y = 8(0) + 123
y = 8
(0, 8)

so y - 123 = (x - 0)

bobbym · 2012-06-27 02:17:17

The points are actually 1,115.00 and 5,83.00.

Aren't those the two choices from the question?

SlowlyFading · 2012-06-27 02:18:34

So instead of 0 I could pick 1,115.00 and then do the same thing?

bobbym · 2012-06-27 02:23:04

Yes, that is what you must do. Now just use the formula I gave you and plug in. Let me know what you get.

SlowlyFading · 2012-06-27 02:39:34

I'm not sure if the answer is y - 123 = 8 (x - 1) but that's what I got.

bobbym · 2012-06-27 02:41:27

You did choose (1,115) didn't you?

SlowlyFading · 2012-06-27 02:44:58

Yes.
What about y - 8920 = 8(x - 1,115) ?

bobbym · 2012-06-27 02:47:18

Hi;

Hold on.

That is the formula and these are the points (1,115).

Which one is

?

SlowlyFading · 2012-06-27 02:49:30

What do you mean "these are the points"? Isn't 1,115 just one point?

bobbym · 2012-06-27 02:51:25

Yes, sorry. I meant the coordinates. Anyway which one of those two numbers is x1?

SlowlyFading · 2012-06-27 02:52:24

1,115 would be x1 right?

bobbym · 2012-06-27 02:55:45

Hi;

An ordered pair that makes up a point is (x1,y1)

Okay, so which one is x1?

Math Is Fun Forum

#1 2012-06-19 03:21:02

Follow-up on my last post

#2 2012-06-19 03:35:25

Re: Follow-up on my last post

#3 2012-06-25 16:33:20

Re: Follow-up on my last post

#4 2012-06-25 19:08:17

Re: Follow-up on my last post

#5 2012-06-26 08:02:11

Re: Follow-up on my last post

#6 2012-06-26 08:09:53

Re: Follow-up on my last post

#7 2012-06-26 16:49:43

Re: Follow-up on my last post

#8 2012-06-26 18:42:49

Re: Follow-up on my last post

#9 2012-06-26 18:59:24

Re: Follow-up on my last post

#10 2012-06-27 02:00:15

Re: Follow-up on my last post

#11 2012-06-27 02:01:39

Re: Follow-up on my last post

#12 2012-06-27 02:12:49

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#13 2012-06-27 02:14:19

Re: Follow-up on my last post

#14 2012-06-27 02:16:13

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#15 2012-06-27 02:17:17

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#16 2012-06-27 02:18:34

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#17 2012-06-27 02:23:04

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#18 2012-06-27 02:39:34

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#19 2012-06-27 02:41:27

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#20 2012-06-27 02:44:58

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#21 2012-06-27 02:47:18

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#22 2012-06-27 02:49:30

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#23 2012-06-27 02:51:25

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#24 2012-06-27 02:52:24

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#25 2012-06-27 02:55:45

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