Math  /  Algebra

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For the given functions, find (fg)(x)(f \circ g)(x) and (gf)(x)(g \circ f)(x) and the domain of each. f(x)=3x+1,g(x)=xf(x)=3 x+1, g(x)=\sqrt{x} 36 (fg)(x)=(f \circ g)(x)= \square

Studdy Solution

STEP 1

What is this asking? We need to find two new functions: *f(g(x))* and *g(f(x))*, and also figure out what values of *x* are allowed for each. Watch out! Square roots can be tricky with negative numbers, so we'll need to keep an eye on the domain!

STEP 2

1. Find *f(g(x))*
2. Find the domain of *f(g(x))*
3. Find *g(f(x))*
4. Find the domain of *g(f(x))*

STEP 3

Let's **start** by remembering what (fg)(x)(f \circ g)(x) *actually means*.
It means we're putting g(x)g(x) *inside* f(x)f(x)!
It's like a function *turducken*!

STEP 4

We know that f(x)=3x+1f(x) = 3x + 1 and g(x)=xg(x) = \sqrt{x}.
So, to find f(g(x))f(g(x)), we **replace** the *x* in f(x)f(x) with the *entire* g(x)g(x) function.

STEP 5

This gives us f(g(x))=3(x)+1f(g(x)) = 3(\sqrt{x}) + 1.
See how we **substituted** x\sqrt{x} for *x*?

STEP 6

Now, the **domain** is all the possible *x* values we can plug in *without breaking math*.
We can't take the square root of a negative number, can we?

STEP 7

So, for x\sqrt{x} to be happy, *x* must be greater than or equal to zero.
That means our **domain** is x0x \ge 0.

STEP 8

Time to flip the script and find (gf)(x)(g \circ f)(x).
Now we're putting f(x)f(x) *inside* g(x)g(x)!

STEP 9

We **substitute** f(x)f(x) which is 3x+13x + 1 into g(x)g(x) which gives us g(f(x))=3x+1g(f(x)) = \sqrt{3x + 1}.

STEP 10

Again, we need to make sure the stuff *inside* the square root isn't negative.
So, we need 3x+103x + 1 \ge 0.

STEP 11

Let's **solve** for *x*! **Subtract** 1 from both sides: 3x13x \ge -1.

STEP 12

Now, **divide** both sides by 3: x13x \ge -\frac{1}{3}.
So, our **domain** is x13x \ge -\frac{1}{3}.

STEP 13

(fg)(x)=3x+1(f \circ g)(x) = 3\sqrt{x} + 1 with domain x0x \ge 0
(gf)(x)=3x+1(g \circ f)(x) = \sqrt{3x + 1} with domain x13x \ge -\frac{1}{3}

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