Oh Fiddlesticks - DPChallenge Forums

01/19/2009 05:45:30 PM · #1

I am having a stupid moment and cannot for the life of me figure out if these two lines are perpendicular. this is stupid math i learned two years ago and for some reason am being asked about it again

the lines are...

y=-2x+22
y=.5x+4.5

oh, and if someone could actually explain to me how this works that would be great. i know this is lame math, im just having a lame blond moment:/

01/19/2009 05:50:44 PM · #2

Lines are perpindicular if their slopes are negative reciprocals. Your lines are in slope-intercept form, y = mx + b, where m is the slope, and b is the y-intercept

A value x has neagtive reciprocal -1/x.

Are your lines perpindicular?

Sony DT 18-70mm f/3.5-5.6 Aspherical ED Zoom Lens for Sony Alpha

01/19/2009 05:53:56 PM · #3

yes?

SoulMan1978

Sony Alpha a55

01/19/2009 05:56:03 PM · #4

Uh, yes they are lol. As they're both linear, the gradient of each is the multiple of x, i.e. -2 and 0.5

01/19/2009 05:57:22 PM · #5

Originally posted by JDubsgirl:

oh, and if someone could actually explain to me how this works that would be great. i know this is lame math, im just having a lame blond moment:/

Slope is rise over run. A slope of 3 = 3/1 means take a point, go to the right 3 steps and then up 1 step. Now connect the points and do it again.

The negative reciprocal of 3 is -1/3. Take a point, go to the LEFT (negative) 1 step and then up 3 steps. (Or you can go to the right 1 step and DOWN (negative) 3 steps -- it doesn't matter if you take the negative sign to be in the numerator or denominator.) This line will be perpindicular to the first.

ETA: Typos! Typing too fast. And yes, they are.

Message edited by author 2009-01-19 18:00:11.

01/19/2009 05:59:35 PM · #6

Originally posted by bvy:

Originally posted by JDubsgirl:

oh, and if someone could actually explain to me how this works that would be great. i know this is lame math, im just having a lame blond moment:/

Slope is rise over run. A slope of 3 = 3/1 means take a point, go to the right 3 steps and to then up 1 step. Now connect the points and do it again.

The negative reciprocal of 3 is -1/3. Take a point, go to the LEFT (negative) 1 step and then up 3 steps. (Or you can go to the right 1 step and DOWN (negative) 3 steps -- it doesn't matter if you take the negative sign to be in the numerator or denominator.) This line will be perpindicular to the first.

yeh i understand slope, i was just having issues applying it for some reason. its like i've have a log jam in my head for the past week

incubus

Canon EOS-5D

01/19/2009 06:14:57 PM · #7

OMG this brings back so many memories, I can barely remeber how to do this stuff anymore. Shows you how much of this stuff you need to know in the real world.

Message edited by author 2009-01-19 18:15:17.

goinskiing

Canon EOS-6D

01/19/2009 06:16:36 PM · #8

Originally posted by SoulMan1978:

Uh, yes they are lol. As they're both linear, the gradient of each is the multiple of x, i.e. -2 and 0.5

That is a naughty word... ;-)

01/19/2009 06:18:10 PM · #9

Originally posted by incubus:

OMG this brings back so many memories, I can barely remeber how to do this stuff anymore. Shows you how much of this stuff you need to know in the real world.

yeh really

01/19/2009 06:20:02 PM · #10

ok one more not-so-stupid question. does anyone know about reciprocal functions? i have this probelm here that states im supposed to find the simplest form of...

f(x)=4/x when x is 4f(x+2)-3.

whaaat?!?!?! does anyone actually understand that? i cant even graph the damn thing let alone say what the simplest form is(i have no idea what it would even look like!!)

01/19/2009 06:26:39 PM · #11

I'm not sure about your phrasing of the problem, but it sounds like you need to plug (x+2) into f(x) -- that is take f(x+2). Then use that result in your second expression and simplify.

01/19/2009 06:30:20 PM · #12

what about the 4 and the -3 in the problem? how do they apply?

01/19/2009 06:38:38 PM · #13

I'd have to see the problem in context. Doesn't make much sense to me the way it's written.

All I can see that you can do with it is take f(x+2) -- if f(x) = 4/x, then f(x+2) = 4/(x+2) -- and substitute into the second expression.

So 4* f(x+2) - 3
= 4[4/(x+2)] - 3
= 16/(x+2) - 3.

And, of course, if asked about the domain, x cannot be equal to zero.

Sony DT 18-70mm f/3.5-5.6 Aspherical ED Zoom Lens for Sony Alpha

01/19/2009 06:40:57 PM · #14

hmmm ok ill mull over that for awhile. thanks for the help

SoulMan1978

Sony Alpha a55

01/19/2009 06:50:54 PM · #15

Originally posted by goinskiing:

Originally posted by SoulMan1978:
Uh, yes they are lol. As they're both linear, the gradient of each is the multiple of x, i.e. -2 and 0.5

That is a naughty word... ;-)

It is? not in advanced editing, surely? ;-)

01/19/2009 06:52:00 PM · #16

Originally posted by SoulMan1978:

Originally posted by goinskiing:

Originally posted by SoulMan1978:
Uh, yes they are lol. As they're both linear, the gradient of each is the multiple of x, i.e. -2 and 0.5

That is a naughty word... ;-)

It is? not in advanced editing, surely? ;-)

LOL!!