SOLUTION: Can I get help with this question please x/x-4;g(x)=-7/x and solve for (fof)(x) Thank you so much

Algebra ->  Functions -> SOLUTION: Can I get help with this question please x/x-4;g(x)=-7/x and solve for (fof)(x) Thank you so much      Log On


   



Question 1016366: Can I get help with this question please
x/x-4;g(x)=-7/x and solve for (fof)(x)

Thank you so much

Answer by ikleyn(52748) About Me  (Show Source):
You can put this solution on YOUR website!
.
Can I get help with this question please
x/x-4;g(x)=-7/x and solve for (fof)(x)
-------------------------------------------------

1. You didn't define f(x) for this problem.

2. You defined g(x) - for what purpose?

------------------------------------------------------
Comment from student: Sorry it was the 1st part f(x)=x/x-4;g(x)=-7/x and solve for (fof)(x) thank you so much
------------------------------------------------------

My responce: OK.

(fof)(x) is the composition, (fof)(x) = f(f(x)).

In other words, you need to substitute x inside f(x) by the expression for f(x) :

(fof)(x) = f(f(x)) = %28x%2F%28x-4%29%29%2F%28%28x%2F%28x-4%29%29-4%29.

The first step is done.

The next step is to simplify what you got.

Let us simplify the denominator separately. For it, write the fractions in the denominator with common denominator:


x%2F%28x-4%29-4 = x%2F%28x-4%29+-+%284%2A%28x-4%29%29%2F%28x-4%29%29 = %28%28x+-+4%2A%28x-4%29%29%2F%28x-4%29%29 = %28-3x%2B16%29%2F%28x-4%29.

Now your composition function is 

(fof)(x) = f(f(x)) = %28x%2F%28x-4%29%29%2F%28%28x%2F%28x-4%29%29-4%29 = %28x%2F%28x-4%29%29%2F%28%28-3x%2B16%29%2F%28x-4%29%29 = x%2F%28-3x%2B16%29.    <----- On the way, you canceled (x-4) in two spots.

The task is completed.