Find all x-values such that f(x)= -4

JeffM said:
First f(x) does not equal - 4. The question asks you to find the specific value or values (if any) of x where f(x) = - 4. Does the question give you a general expression for f(x) or just the graph. Looking at the graph, what, if any, non-negative values of x can result in a negative value of f(x)? Does it look as those there are multiple values of x where f(x) = - 4? Does the graph give any clues about a value for x where f(x) = - 4?
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I'm not sure I understand, hence why I asked the question.

The value of x has to equal a negative number in the x-axis, I think
It can't be a non negative value.

That, or there is no solution.


As I said, I have no idea how this particular shape of graph works.
x could equal to -2 or it could equal to -1 and -2, or it could be infinity.
I don't know.
 
JeffM said:
Do you know how to read a graph? Each point on the graph tells pictorially what value of y corresponds to what value of x and vice versa. That is the basic purpose of a graph.

If y = f(x), that means for each value of x WITHIN THE DOMAIN OF THE FUNCTION there is exactly ONE value of y. So when you are asked what f(-2) equals, there is exactly one answer if -2 lies in that domain. HOWEVER, for each value of y WITHIN THE RANGE OF THE FUNCTION f(x) = y, there is AT LEAST ONE value of x, but perhaps more, such that f(x) = that specific value of y. So when you are asked what values of x result in f(x) equalling - 4, the answer may be one, more than one but finite, or infinite.

Now in the previous link, you learned I hope that f(x = - 2) = - 4. So you should be able to see AT LEAST one value of x for which f(x) = -4. What is it? Now LOOK at that graph. Do you or do you not see any other values of x such that f(x) = - 4? If you do, what are they? If not, how many values of x will you give in your answer?

This problem is basically asking you to interpret a graph and relate it to concept of a function.
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No, I do not know how to read THIS particular graph.

Understanding f(-2) was easier because it only contains one value

For the f(x)= -4, I know for sure that one of the points is -2....maybe the other point is zero? or -1
I don't know.
 
JeffM said:
When you are asked where is f(x) = some number, say a, draw the line y = a. Every place that line intersects the graph of f(x) represents a value of x such that f(x) = a. Provided that the range of f(x) includes a, there will be at least one point of intersection, and there MAY OR MAY NOT be more.

What is confusing to you about THIS particular graph.
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Uh-huh, so it's only -2 after all

It confused me because ALL of the other graphs we had have more than 1 value for x
Plus in the question the teacher provided it says use comas to separate numbers so i quickly assumed it's
more than one number.

Thanks for helping~
 
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