# Question: Functions f and g

## Comment on Functions f and g

### Thank you very much for the

Thank you very much for the tutorial, it was very helpful. Could you please help me understand when questions like these end? To clarify, in the beginning I thought the question was done when we discovered that K = -5﻿

### That's a common trick the

That's a common trick the GMAT test-takers like to pull. We THINK the goal is to find the value of k, but we ACTUALLY need to find the value of f(k+1)

### Hi Brent, as you mentioned we

Hi Brent, as you mentioned we ACTUALLY need to find the value of f(k+1), which is -4 but then why is the need to substitue into f(x) = 3x + 1 again? Thanks Brent.

### Be careful. The value of k+1

Be careful. The value of k+1 is not the same as the value of f(k+1).

Once we learn that k = -5, our goal is to find the value of f(k+1)
So, when we replace k with -5, we get: f(k + 1) = f((-5) + 1) = f(-4)

So, we still need to find the value of f(-4)
Since f(x) = 3x + 1, we know that f(-4) = 3(-4) + 1, which equals 11.

Does that help?

### Thanks Brent for great

Thanks Brent for great explanation. As is f(-4) rather than -4 itself, therefore it's a sign that it still need substituting back into f(x) to get an integer on it own in this type of function questoin? Is my understanding correct? Thanks Brent

That's correct.

### Hi. I want more practice with

Hi. I want more practice with questions of this type and difficulty. Can you direct me? I typed in function notation practice on google. But they aren't of this difficulty. They are easier.

### We have links to functions

We have links to functions questions in the Reinforcement Activities box here: https://www.gmatprepnow.com/module/gmat-algebra-and-equation-solving/vid...

### Hi Brent,

Hi Brent,

Just a quick question. Why can't I solve for k by equating f(k+1) = g[(k+1)/2] and then solve it? Theoretically, it should be the same right?

### That approach will kind of

That approach will kind of work, but you will be forced to perform some VERY TRICKY mental maneuvering during the solution.

Try it and you'll see.

Cheers,
Brent