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Comment on Function Notation
Hi Brent,
I'm a touch confused with something. I was doing one of the early reinforcement questions and it asked:
If f(x) = 3x − √x and g(x) = x^2, what is f(g(4))?
How exactly do you read out "f(g(4))"? I was confused as to what exactly the question was asking? It seems to me that is asking 'what is f(x) if g(4)?". Is that correct? The problem is that I couldn't see that until I saw your solution in the GMAT Club forums.
Here's the link to the question: https://gmatclub.com/forum/if-f-x-3x-x-and-g-x-x-2-what-is-f-g-209750.html
Thanks for any help,
Yusuf
Question link: https:/
Question link: https://gmatclub.com/forum/if-f-x-3x-x-and-g-x-x-2-what-is-f-g-209750.html
The notation f(g(4)) represents the value of the function (f) when we input the value of g(4)
So, in this example, g(4) = 4² = 16
So, f(g(4)) = f(16) [now we must evaluate f(16)]
f(16) = 3(16) − √16
= 48 - 4
= 44
So, to recap, f(g(4)) = f(16) = 44
Does that help?
Cheers,
Brent
Awesome! That confirms my
Hi Brent,
Could you please help me to solve the following questions taken from a practice test?
For which of the following functions is f(a + b) = f(a) + f(b) for all positive numbers a and b ?
f(x) = x^2
f(x) = x + 1
f(x)= sqrt{x}
f(x)= 2/x
f(x) = –3x
Thank you!
I'm happy to help.
I'm happy to help.
Here's my full solution: https://gmatclub.com/forum/for-which-of-the-following-functions-is-f-a-b...
Cheers,
Brent
Hi Brent,
I'm lost in example:
https://gmatclub.com/forum/the-functions-f-and-g-are-defined-as-f-x-2x-3-and-g-x-x-293530.html
How does F(x) = F(y)? Was there a mistake in the question and it should have stated F(x) in the last part of the question?
Thanks,
Marc
Question link: https:/
Question link: https://gmatclub.com/forum/the-functions-f-and-g-are-defined-as-f-x-2x-3...
If f(x) = 2x – 3, then f(7) = 2(7) – 3
And f(19) = 2(19) – 3
And f(5.5) = 2(5.5) – 3
....and f(y) = 2y – 3
The main idea here is that we can input anything into the function named "f"
The function, f, tells us to take the inputted value, double it and then subtract 3.
So, we can also say that....
f(14) = 2(14) – 3
And f(k²) = 2(k²) – 3
And f(4q + 1) = 2(4q + 1) – 3
Does that help?
Cheers,
Brent
Hi Brent,
I actually get confused when there are complex functions like these- f(4x) = 8x² − 1
In a simpler equations - f(x) = x^2, we know that the value in the bracket is going to be placed where X is on the RHS.
But in this f(4x) = 8x² − 1, does it mean that the value of x in the LHS will be replaced on the RHS. In short, I am not not able to understand the meaning of such equations.
Thanks,
Erik
I believe you're referring to
I believe you're referring to this super difficult question: https://gmatclub.com/forum/if-f-x-is-a-function-what-is-the-value-of-f-2...
As you suggested, in MOST cases, the function looks something like f(x) = x²
So, f(3) = 3² = 9
And f(-11) = (-11)² = 121
And even f(x + 5) = (x + 5)² = x² + 10x + 25
That said, the function f(4x) = 8x² − 1 isn't much different from the function g(k) = 8k² − 1
To find the value of g(3), we replace k with 3 to get: g(3) = 8(3²) − 1 = 71
However, since f(4x) requires us to multiply the x-value by 4, we must do a little work before we can find the value of f(3)
To find the value of f(3), we need to first find the value of x such that 4x = 3.
Since x = 0.75 is the solution to the equation 4x = 3, we can know that, in order to evaluate f(3), we need x to be 0.75
In other words, f(3) = f[(4)(0.75)] = 8(0.75²) − 1 = 4.5 - 1 = 3.5
Does that help?
Hey Brent,
For this question: https://gmatclub.com/forum/for-all-integers-n-the-function-f-is-defined-by-f-n-a-n-where-a-97735.html
How do we know that we need to square/cube it
Question link: https:/
Question link: https://gmatclub.com/forum/for-all-integers-n-the-function-f-is-defined-...
We're told that f(n) = a^n.
So, for example, f(1) = a^1
And f(2) = a^2
And f(3) = a^3
And f(4) = a^4
.....etc.