# Thread: Function, determine point on graph: If f(-5) = -2 & g(x) = -2*f(x), what point can...

1. ## Function, determine point on graph: If f(-5) = -2 & g(x) = -2*f(x), what point can...

Hi there,
I am very new to this forum and I would appreciate some help to understand how to solve this simple function.
It is part of some homework. I am not looking for the solution but for help. Looks like I have stones in the head!

Schermata 2017-04-12 alle 18.57.10.jpg

Thank you

2. Originally Posted by Millone
I am very new to this forum and I would appreciate some help to understand how to solve this simple function.
It is part of some homework. I am not looking for the solution but for help. Looks like I have stones in the head!

If f(5) = 2 and
g(x) = 2f(x), what point can you determine on the graph of g?

1) -63, 6
2) -5,
-4
3) -8, -2
4) 6, 7
5) 12, 1
It looks like this exercise contains a sign error.

I have highlighted in red (above) three negative signs. Please confirm that each of those three negative signs appear in the materials that you were provided.

Do you understand function notation? That is, do you know the meaning of the statement f(-5)=-2?

Also, when we write the coordinates of a point, we enclose them in parentheses.

(-63, 6)
(-5, -4)
etc...

3. Hi,
yes I confirm the negative values. Your help will be appreciated.

Schermata 2017-04-12 alle 18.57.10.jpg

4. If all we know is that f(-5)= -2 and that g(x)= -2f(x) then the only value of x for which we can calculate g(x) is the value of x for which we calculate f(x) which is x= -5. And g(-5)= -2f(-5)= what?

5. Originally Posted by HallsofIvy
If all we know is that f(-5)= -2 and that g(x)= -2f(x) then the only value of x for which we can calculate g(x) is the value of x for which we calculate f(x) which is x= -5. And g(-5)= -2f(-5)= what?
Thanks.
It is what I thought but that would give me 2f(-5)=10.
I do not have the option (-5, 10) within the range of given answers.
I think I am really missing something.

6. Originally Posted by mmm4444bot
It looks like this exercise contains a sign error.

I have highlighted in red (above) three negative signs. Please confirm that each of those three negative signs appear in the materials that you were provided.

Do you understand function notation? That is, do you know the meaning of the statement f(-5)=-2?

Also, when we write the coordinates of a point, we enclose them in parentheses.

(-63, 6)
(-5, -4)
etc...
I do understand the function notation. I think I also understand the statement f(-5)=-2 "return -2 for input -5"
So the equation could be simply the equivalent of f(x)=x+3 for x=-5.

Having said that, I think that the second equation should be calculated assuming x=-5 which gives me:
g(x)=2f(
x)
g(-5)=-2*f(-5)
=10
I do not have (-5, 10) in the available results to chose.
Thanks for helping

=

7. Originally Posted by Millone
yes I confirm the negative values.
You need to pay closer attention. You confirmed the negative sign in front of the four in (-5,-4), and then you edited your post to remove it!

8. Originally Posted by Millone
I do understand the function notation. I think I also understand the statement f(-5)=-2 "return -2 for input -5"

Good. You understand that the symbol f(-5) can be replaced with the value -2.

Having said that, I think that the second equation should be calculated assuming x=-5 which gives me:
g(x)=2f(x)
g(-5)=-2*f(-5)
=10
Why are you multiplying (-2)(-5)?

The symbol f(-5) equals -2, not -5.

-5 is the input to function f, and -2 is the output.

-2*f(-5) means multiply the output by -2.

(-2)(-2) = 4

9. Originally Posted by mmm4444bot

Good. You understand that the symbol f(-5) can be replaced with the value -2.

Why are you multiplying (-2)(-5)?

The symbol f(-5) equals -2, not -5.

-5 is the input to function f, and -2 is the output.

-2*f(-5) means multiply the output by -2.

(-2)(-2) = 4

Thank you. It is clear now.