[SOLVED] need a lil help figuring out a problem

• Feb 14th 2009, 02:11 AM
ninobrn99
[SOLVED] need a lil help figuring out a problem
Supposed the point (2,4) is on the graph of y=f(x). Find a point on the graph of the given function

1) y=f(x+1)
a)(2,3)
b) (1,4)
c) (2,5)
d) (3,4)

2)y=f(x)+8
a) (2,-8)
b) (-6,4)
c) (2,12)
d) (10,4)

Im not looking for the answer, but rather how to solve the problems. I can't find a similar one in my book.
• Feb 14th 2009, 02:46 AM
mr fantastic
Quote:

Originally Posted by ninobrn99
Supposed the point (2,4) is on the graph of y=f(x). Find a point on the graph of the given function

1) y=f(x+1) Mr F says: Substitute x = 1 and what have you got ....?
a)(2,3)
b) (1,4)
c) (2,5)
d) (3,4)

2)y=f(x)+8 Mr F says: Substitute x = 2 and what have you got ....?
a) (2,-8)
b) (-6,4)
c) (2,12)
d) (10,4)

Im not looking for the answer, but rather how to solve the problems. I can't find a similar one in my book.

..
• Feb 14th 2009, 03:53 AM
HallsofIvy
You only know f(2) so you must turn whatever you have into '2'. That is the point of mr fantastic's suggestion: if x= 1, then x+1= 2 so f(x+1)= f(2).
• Feb 14th 2009, 11:39 AM
ninobrn99
sorry, im still not getting it. Maybe I need the problem worked so I can see the steps. I was up till 3am working on this stuff (Doh)
• Feb 14th 2009, 12:05 PM
mr fantastic
Quote:

Originally Posted by ninobrn99
sorry, im still not getting it. Maybe I need the problem worked so I can see the steps. I was up till 3am working on this stuff (Doh)

x = 1: y = f(1 + 1) = f(2). But you know f(2) = 4. Therefore a point on the graph of y = f(x+1) is (1, 4).

Try the other one now.
• Feb 14th 2009, 12:23 PM
ninobrn99
Quote:

Originally Posted by mr fantastic
x = 1: y = f(1 + 1) = f(2). But you know f(2) = 4. Therefore a point on the graph of y = f(x+1) is (1, 4).

Try the other one now.

Im not sure if I'm making sense, but here's what Im getting:

f(x) is a constant which is why when x=1, y=4 and when x=2, y=4

since the next problem is linear, [f(2)=4] + 8 therefore, the answer to
f(x)+8 is (2,12)

Is that at all close?
• Feb 14th 2009, 12:35 PM
HallsofIvy
No one has told you that f(1)= 4! mr fantastic told you that if x= 1 then f(x+1)= f(2)= 4. That tells you nothing about f(1).

You are told initially that f(2)= 4. That is the only value of f you know and so is the only value you [b]could[\b] get.

You are however correct that f(2)+ 8= 4+ 8= 12 because, again, you are working with f(2).
• Feb 14th 2009, 12:43 PM
ninobrn99
Thank you both. It's starting to make sense. I've got three word problems left, I'll try my best to knock them out on my own, if not, Im posting back up :)