Sign in to follow this  
subflood

v-shaped vertices

Recommended Posts

subflood    170
I don't understand equations like this: y = |x + 2| I know you subtract 2 so you can get rid of the posotive 2 but why do you do that and where does the 2 go? When you graph this I know you move the vertix two places to the left but why? I really don't undeerstand these at all.

Share this post


Link to post
Share on other sites
Eelco    301
Quote:
Original post by subflood
I don't understand equations like this: y = |x + 2|

I know you subtract 2 so you can get rid of the posotive 2 but why do you do that and where does the 2 go? When you graph this I know you move the vertix two places to the left but why? I really don't undeerstand these at all.

i really dont understand you at all either.

Share this post


Link to post
Share on other sites
siaspete    208
I guess he's talking about graphs of functions.

y = x, makes a diagonal line right?

y = |x| makes a v-shape, reflecting at the y axis.
e.g.
|2| = 2.
|-2| also = 2.

y = x + 2 makes a diagonal line offset by 2

So y = |x + 2| makes a V-shape, offset by 2.

Hope this helps
Pete

Share this post


Link to post
Share on other sites
Eelco    301
Quote:
Original post by subflood
"So y = |x + 2| makes a V-shape, offset by 2."

but shouldn't the point on the line be (2, 0) instead of (-2, 0)?

no.

just fill in the values and youll see its right.

|x+2| = 0 -> x = -2

im sorry but i think this is a (bluntly put) stupid question. this forum is supposed to be about math as it relates to gamedev, if there is anything this relates to its elementary school.

Share this post


Link to post
Share on other sites
Eelco    301
Quote:
Original post by subflood
why |x + 2| = 0? why not |x + 2| = 5

sigh.

were looking for a point on the x-axis, ie y = 0

y = |x + 2| = 0

Share this post


Link to post
Share on other sites
Guest Anonymous Poster   
Guest Anonymous Poster
To subflood:
You can see the problem more clearly if you decomposed it into two equations

y = x + 2 for all x+2 >= 0 -> x >= -2

and

y = - (x + 2) for all –(x + 2) >= 0 -> x <= -2

so you are correct the equation is a V shape line centerd at the point (-2, 0)

Share this post


Link to post
Share on other sites
ajas95    767
Quote:
Original post by Eelco
im sorry but i think this is a (bluntly put) stupid question.


I don't think it's a stupid question, I just think it's being asked in a stupid way. It is a little counter-intuitive,
given the graph of y = |x|:

y = |x| + 2 shifts it UP 2 units, while
y = |x + 2| shifts it LEFT 2 units.

Why is that? I think is what he's asking. Without looking at the graphs or really thinking about it, you might guess that if y = |x|+2 shifted it up, then y = |x+2| should shift it right. The same principle applies to graphing ellipses, hyperbola, or any graph, so it is important. Just like while |x|*2 makes it stretch upward, |x*2| makes it compress sideways.

You can think of it like (still using y = |x| as the baseline), now think about x = 0. you have y = |0|. Now for x + 2 to produce that same result, it has to be 2 Fewer, so you get |(-2) + 2| = |0|. So for that same value of y, x is 2 fewer than in the y = |x| graph.

It makes sense when you think "x + 2 doesn't actually add 2 to the x you're graphing, rather it subtracts 2 from the value that x has to be to produce the same result as if x were alone" strange but true.

Share this post


Link to post
Share on other sites
grhodes_at_work    1385
Folks,

This question is off topic, too close to schoolwork. I'm glad subflood understands the problem, but there are other places (actual school in real life, websites dedicated to homework) that are more appropriate for this type of question. This forum has a policy that discourages this type of question, when it is not qualified. Please review the Forum FAQ for details.

I'm closing the thread per forum policy.

Share this post


Link to post
Share on other sites
Guest
This topic is now closed to further replies.
Sign in to follow this