umm...am i dumb or is something wrong here?

[ManBearPig]

my roomate and i both thought that if you have a graph f(x) and its transformed to f(x+2) it move RIGHT 2 units...but everywhere i look online it says it moves left. wtf? uhhh

 

[compnovice]

What if f(x)=polynomial?

 

[DaveSimmons]

U R DUM!

At what values of x do the 2 functions cross y=0 ? y=10?

Hint: it's sooner for y = (x+2) than for y = (x + 0)

(i.e. graph a simple linear function or two to convince yourself)

 

[ManBearPig]

thats so weird, i wonder why i was thinking that. maybe because f(x)+2 is up and f(x)-2 is down so i took + to mean right and - to mean left.

 

[ManBearPig]

wtf now im looking thru my notes and it says: the graph of y=f(x-k) is the graph of y=f(x) shifted to the right by k units if k is positive and to the left by k units if k is negative.

 

[ManBearPig]

so htf do you do horizontal shifts? one source says follow your intuition and the other says do the opposite.

 

[DaveSimmons]

Originally posted by: Kazaam
wtf now im looking thru my notes and it says: the graph of y=f(x-k) is the graph of y=f(x) shifted to the right by k units if k is positive and to the left by k units if k is negative.

Because it is x - k. So if "k is negative," say -2, then it is x - (-2) = x + 2.

If "k is positive," say +2, then it is x - (+2) = x - 2.

You just confused yourself with a double negative.

 

[ManBearPig]

oh, i think i get it, thanks. So then i was right, (x-2) would be two units left of just "x" and (x+2) would be two units right of just "x"?

thanks a lot...i dunno how i forgot this

 

[Inferno0032]

It's opposite, that simple. Negative usually means move RIGHT. + means move LEFT.

 

[DaveSimmons]

No -- your notes said f(x - 2) is 2 units right and your notes are correct.

Look up, we showed earlier that f(x + 2) moves the graph left.

f(x + 2) = left by 2
f(x - 2) = right by 2

f(x + k) = left by k if k is positive ( >= 0)
f(x - k) = right by k if k (the number being subtracted) is >= 0.

k being positive = 1, 2, 3
k being negative = -1, -2, -3.

If k is negative it reverses the direction :
f (x + (-2) ) = f (x - 2)
f (x - (-2) ) = f ( x - - 2) = f ( x + 2)

 

[imported_Baloo]

Do we have the option to, yes, you're dumb and there is something wrong here?

 

[DrPizza]

How about a circle?

(x-2)^2 + (y+3)^2 = 25
Center (2,-3) radius 5. Think about which way it gets moved.

If you agree that y = x^2 + 10 is a parabola moved up by 10 units, rewrite it as
(y-10)=x^2. Ahhhh, again, change the sign.

-- -- - - - - --

Now, lets look at y=x^2, and a table of values
x|y
----
1|1
2|4
3|9
4|16

And, compare y = (x-2)^2 to it.

x|y
----
1|1
2|0
3|1
4|4
5|9
6|16

Note: the x values that are 2 greater have the same y values as before. Hence, it's shifted to the RIGHT for x-2. Why? Because (12-2)^2 is the same as (10)^2. You need values that are 2 greater than before in order to get the same y values.

 

[hdeck]

a circle isn't a function!

 

[thepd7]

Originally posted by: DrPizza
How about a circle?

(x-2)^2 + (y+3)^2 = 25
Center (2,-3) radius 5. Think about which way it gets moved.

If you agree that y = x^2 + 10 is a parabola moved up by 10 units, rewrite it as
(y-10)=x^2. Ahhhh, again, change the sign.

-- -- - - - - --

Now, lets look at y=x^2, and a table of values
x|y
----
1|1
2|4
3|9
4|16

And, compare y = (x-2)^2 to it.

x|y
----
1|1
2|0
3|1
4|4
5|9
6|16

Note: the x values that are 2 greater have the same y values as before. Hence, it's shifted to the RIGHT for x-2. Why? Because (12-2)^2 is the same as (10)^2. You need values that are 2 greater than before in order to get the same y values.

Teacher to the rescue!

 

[Shawn]

it moves to the left

 

[Schfifty Five]

f(x) = x + 5
f(3) = 3 + 5 = 8

f(x+2) = (x+2) + 5
For what value of x will f(x+2) = 8?

8 = x+2+5, therefore, x = 1.

Now can you see why the graph of f(x+2) is shifted TO THE LEFT BY 2?

 

[Acanthus]

You think thats fun, try calculating the surface area of an oval based cone.

 

[DrPizza]

Originally posted by: hdeck
a circle isn't a function!

Congratulations for pointing that out. Did someone say it was, or imply it was?

 

[legoman666]

get a god damn ti83 and plot a few graphs and find out.