Math question

Onkel Neal · 04-13-12, 04:42 PM

Ok, so I am refreshing myself with some math. I am going over Slope-Intercept Form of a line

y=mx+b

and,

"point-slope" form of the equation

Is this the same thing? I guess not.

And then you have General Form, Ax + By + C = 0
What's the C? It seems to be missing from the other formulas

As well as the A & B?

vienna · 04-13-12, 04:52 PM

Just reading that gave me the same mind-numbing, out-of-body feeling I used to get in high school...

Thanks for the cheap high, Neal...

(Oh, and if I remember correctly, the answer is always "B"...)

...

Gargamel · 04-13-12, 09:07 PM

They are the same. *Just solve for y.

Ax + By +C = 0

Becomes

y = -(A/B)x -(C/B)

So in y=mx+b

m = -(A/B)
And
b= -(C/B)

(note upper/lower case)

the_tyrant · 04-13-12, 09:11 PM

use wolfram alpha (http://worlframalpha.com)

it is a math student's best friend

Gargamel · 04-13-12, 09:22 PM

Except for when I'm trying to use it to estimate the cost of welding jobs. When I ask for the mass of given volume of steel, it gives me the price of steel futures. Wtf ?

It wont help him learn how the equation works either.

Onkel Neal · 04-13-12, 10:34 PM

Quote:

Originally Posted by Gargamel

They are the same. *Just solve for y.

Ax + By +C = 0

Becomes

y = -(A/B)x -(C/B)

So in y=mx+b

m = -(A/B)
And
b= -(C/B)

(note upper/lower case)

How did it become that second line?

Ax + By +C = 0

Subtract C from both sides:
Ax + By = -C

Subtract Ax from both sides:
By = -C -Ax

Divide both sides by B:
y = (-C -Ax)/B

How does it become:
y = -(A/B)x -(C/B) ??

I have been watching instructional videos which are great except often the person who KNOWS how to do this forgets the pupil does NOT and assumes he does.

For example, bang! Where did out friends A, B, and C disappear to??

U570 · 04-13-12, 11:06 PM

Ax+By+C=0 then
By= -Ax-C and then
y=-(Ax/B)-(C/B)
-(Ax/B) is just the same as -(A/B)x
and here we have:
y=-(A/B)x-(C/B)
I hope this solve your dilemma Neal.

Onkel Neal · 04-13-12, 11:09 PM

Yes, thanks, I just have to do about 300 examples to imprint it in my brain.

I learned this stuff about 4 times in my life... but it never gets used.

nikimcbee · 04-17-12, 07:04 PM

You lost me at the word math.

Sailor Steve · 04-17-12, 08:25 PM

Okay, I bookmarked the Khan thing. I'll try to see if I can learn anything.

04-13-12, 04:42 PM	#1
Onkel Neal Born to Run Silent Join Date: Jan 1997 Location: Cougar Trap, Texas Posts: 21,383 Downloads: 541 Uploads: 224	Math question Ok, so I am refreshing myself with some math. I am going over Slope-Intercept Form of a line y=mx+b and, "point-slope" form of the equation Is this the same thing? I guess not. And then you have General Form, Ax + By + C = 0 What's the C? It seems to be missing from the other formulas As well as the A & B?

04-13-12, 04:52 PM	#2
vienna Navy Seal Join Date: Jun 2005 Location: Anywhere but the here & now... Posts: 7,711 Downloads: 85 Uploads: 0	Just reading that gave me the same mind-numbing, out-of-body feeling I used to get in high school... Thanks for the cheap high, Neal... (Oh, and if I remember correctly, the answer is always "B"...) ... __________________ __________________________________________________ __

04-13-12, 09:07 PM	#3
Gargamel Lucky Sailor Join Date: Oct 2010 Location: Rome Posts: 4,273 Downloads: 81 Uploads: 0	They are the same. *Just solve for y. Ax + By +C = 0 Becomes y = -(A/B)x -(C/B) So in y=mx+b m = -(A/B) And b= -(C/B) (note upper/lower case) __________________ Luck is a residue of Design.

04-13-12, 09:11 PM	#4
the_tyrant Admiral Join Date: Jun 2010 Location: Canada Posts: 2,272 Downloads: 58 Uploads: 0	use wolfram alpha (http://worlframalpha.com) it is a math student's best friend __________________ My own open source project on Sourceforge OTP.net KGB grade encryption for the rest of us

04-13-12, 09:22 PM	#5
Gargamel Lucky Sailor Join Date: Oct 2010 Location: Rome Posts: 4,273 Downloads: 81 Uploads: 0	Except for when I'm trying to use it to estimate the cost of welding jobs. When I ask for the mass of given volume of steel, it gives me the price of steel futures. Wtf ? It wont help him learn how the equation works either. __________________ Luck is a residue of Design.

04-13-12, 11:06 PM	#7
U570 Grey Wolf Join Date: Sep 2011 Location: Planet Earth Posts: 867 Downloads: 89 Uploads: 0	Ax+By+C=0 then By= -Ax-C and then y=-(Ax/B)-(C/B) -(Ax/B) is just the same as -(A/B)x and here we have: y=-(A/B)x-(C/B) I hope this solve your dilemma Neal. __________________ "Submariners are a bunch of intelligent misfits that somehow seem to get along, understand each other and work well together"- Anon

04-13-12, 11:09 PM	#8
Onkel Neal Born to Run Silent Join Date: Jan 1997 Location: Cougar Trap, Texas Posts: 21,383 Downloads: 541 Uploads: 224	Yes, thanks, I just have to do about 300 examples to imprint it in my brain. I learned this stuff about 4 times in my life... but it never gets used.

04-17-12, 07:04 PM	#9
nikimcbee Fleet Admiral Join Date: Jul 2003 Location: Patroling the Slot. Posts: 17,952 Downloads: 90 Uploads: 0	You lost me at the word math. __________________

04-17-12, 08:25 PM	#10
Sailor Steve Eternal Patrol Join Date: Nov 2002 Location: High in the mountains of Utah Posts: 50,369 Downloads: 745 Uploads: 249	Okay, I bookmarked the Khan thing. I'll try to see if I can learn anything. __________________ “Never do anything you can't take back.” —Rocky Russo

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