Given f(x) = 3x, evaluate f(x - 4)? I don't know what to do.

Question

 In a course online. No physical teacher to teach me so what do I do? Answer?

Answer 1

This problem describes a transformation -- a new function based on the old one.  It may be confusing because the problem uses x in both function descriptions.  Let's write:  f(x) = 3x as f(z) = 3z.

 

Now, if z = x-4, what is f(z) ?

   f(z) = 3z,    but z=x-4

   f(z) = f(x-4) = 3(x-4)

   f(z) = f(x-4) = 3x -12

 

The transformation is that f(z) is always 12 less than the original f(x).  That means it is always 12 units lower on a graph of f(x) or f(z) versus x.

Answer 2

f(x) = 3x

f(x - 4) = 3(x - 4)

f(x - 4) = 3x - 12

Answer 3

This is not as bad as it looks. It is really a plug it in question. So any time you see an x in the equation, you put an x-4 instead:

 

f(x)=3x

f(x-4)=3(x-4)

f(x-4)=3x-12

Answer 4

So you have a function f(x) = 3x. They ask you to evaluate f(x-4). Every time you see an x in f(x) = 3x, you are going to put (x-4).

 

f(x-4) = 3 (x-4)

f(x-4) = 3(x)-3(4) distributive property

f(x-4) = 3x-12

 

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