My son is have issue w/ "Determine f(9/2) for the function f(x)= 3X - 5."

[Link82]

My son is have issue solving this he is confused

The Question states Determine f(9/2) for the function f(x)= 3X - 5.

 

[Otis]

The Question states Determine f(9/2) for the function f(x)= 3X - 5.

First, a note about typing an upper-case X. The symbol for the input variable is x, as shown in f(x), so use a lower-case x everywhere. Do not interchange symbols x and X, as those are two different symbols in algebra.

Is your son able to show us what he tried (or explain which part he does not understand)?

I'm wondering whether your son understands the concepts of "function" and "function notation".

f(x) is function notation, and so is f(9/2); these are different ways of writing y, in the following relationship.

y = 3x-5

The letter f in the notation is the name given to the function. In other words, the symbol f does not represent a number. It's handy to assign names to functions, especially when dealing with multiple functions at once.

Symbol x is the input variable, and symbol f(x) is the output variable.

The notation f(9/2) represents the specific output of function f, when the value of the input is 9/2. The value of the input appears inside the parentheses, in function notation. So, x=9/2, in this exercise.

Therefore, the exercise is asking what number comes out of function f when the number 9/2 goes in. Your son needs to substitute the given value for x into the expression 3x - 5, and then he needs to do the resulting arithmetic to come up with the resulting value.

Your son can read more about function notation, by googling the question: what is function notation? :cool:

 

[ksdhart2]

Well, since mechanically this problem is a matter of what might be called "plug-n-chug," any confusion your son is having is likely related to understanding what a function really is and what it does. Essentially, you can think of a function as a "machine" that takes in a number, performs some process, then returns the result. For any number you give it, you will get exactly one number as a result. In the case of this specific problem, the process is 3x - 5. Or, reading that in words, "Multiply (given number) by 3, then subtract 5." So, what would happen if you "fed" the "machine" the number 1? What about the number 2? What about the number 9/2?

 

[Otis]

I like that ksdhart2 mentioned the machine model of a function. It's a good visualization, to think of a functional relationship between x and y as sort of a number-crunching machine. You put values of x in, and the related values of y come out. Here's a simple diagram, to illustrate this model.

In this diagram, the number 4 goes in, and the number 11 comes out. The number-crunching part is that this particular function doubles the input and then adds 3 more: 2(4)+3=11.

This diagram does not, however, utilize function notation for the output variable. It simply uses symbol y.

If we wanted to, we could use function notation. The given relationship between x and y is that y always equals 2x+3. Let's call this function "g". Then, to define function g, we would write:

g(x) = 2x + 3

and to show the specific output of 11, when the input is 4, we would write:

g(4) = 11

 

[Steven G]

The Question states Determine f(9/2) for the function f(x)= 3X - 5.

f(x) = 3x-5, What does f do to x? Just look at the right hand side. It multiplies x by 3 and subtracts 5. If you can say it in words you got it. Again, the rule for f is to multiply x by 3 and subtract 5.

In f(9/5), x is replaces by 9/5. So what does f do to 9/5? It multiplies it by 3 and subtracts 5.

That is, f(9/5) = 3(9/5) -5. Continue from here...

 

[Otis]

f(9/5) = 3(9/5) -5. Continue from here...

Is f(9/5) another practice example or a typo?

 

[Deleted member 4993]

Is f(9/5) another practice example or a typo?

If you look at 5 - standing on your head - just at the right angle and with a mirror - it does look like a 2!!!

 

[Steven G]

If you look at 5 - standing on your head - just at the right angle and with a mirror - it does look like a 2!!!

Thank you.

 

[Steven G]

Is f(9/5) another practice example or a typo?

Typo.

 

[Steven G]

Corner for 9/2 minutes...

I'll admit that's funny