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Math

Math Snap

PROBLEM

Let f(x)=3xf(x) = 3^{-x}. Find f(x)f'(x).

STEP 1

What is this asking?
We need to find the derivative of the function f(x)=3xf(x) = 3^{-x}, which means we're looking for the instantaneous rate of change of f(x)f(x) at any given xx.
Watch out!
Negative exponents can be tricky!
Don't forget the chain rule, and remember your exponent rules.

STEP 2

1. Rewrite with e
2. Apply the chain rule
3. Simplify

STEP 3

Let's rewrite our function f(x)=3xf(x) = 3^{-x} using the magical number e!
Remember, we can rewrite any exponential function axa^x as eln(a)xe^{\ln(a) \cdot x}.
Why? Because eln(a)=ae^{\ln(a)} = a!
It's like a secret code!

STEP 4

So, for our function, we have f(x)=3x=eln(3)(x)=eln(3)xf(x) = 3^{-x} = e^{\ln(3) \cdot (-x)} = e^{-\ln(3) \cdot x}.
See how we brought that negative sign out front? Clean and crisp!

STEP 5

Now, it's chain rule time!
Remember, the chain rule says that the derivative of a composite function like eu(x)e^{u(x)} is eu(x)u(x)e^{u(x)} \cdot u'(x).
It's like peeling an onion, layer by layer!

STEP 6

In our case, u(x)=ln(3)xu(x) = -\ln(3) \cdot x, so u(x)=ln(3)u'(x) = -\ln(3).
See? The derivative of xx is just 1, and the ln(3)-\ln(3) is just a constant hanging out.

STEP 7

Putting it all together, we get f(x)=eln(3)x(ln(3))f'(x) = e^{-\ln(3) \cdot x} \cdot (-\ln(3)). Boom!

STEP 8

Let's make this look nice and tidy.
Remember how we rewrote 3x3^{-x} as eln(3)xe^{-\ln(3) \cdot x}?
Well, now we can switch it back!

STEP 9

So, we have f(x)=3x(ln(3))f'(x) = 3^{-x} \cdot (-\ln(3)).
We can write this even more neatly as f(x)=ln(3)3xf'(x) = -\ln(3) \cdot 3^{-x}. Perfect!

SOLUTION

The derivative of f(x)=3xf(x) = 3^{-x} is f(x)=ln(3)3xf'(x) = -\ln(3) \cdot 3^{-x}.

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