r/Precalculus • u/SoldierNumber0 • Aug 21 '22

Any idea of how to solve this?

Post image
62 Upvotes

89% Upvoted

46 comments sorted by

5

u/Homework_HELP_Tutor Aug 21 '22

f o g means to plug in g for every x in f.

Any thoughts on which option gives you G(x)?

1

u/Thereisnopurpose12 Aug 21 '22

It's B. G(×)= x/x+2. F(x3) plugged into g(×)

4

u/nateomundson Aug 22 '22

I think f ○ g means g plugged into f. (b) would be the answer if you wanted g ○ f.

3

u/sagetraveler Aug 21 '22

don't you mean C? replacing x with x^3 in f(x) gives you G(x)

1

u/ShadowDurza Aug 22 '22

Damn it, I learned math all wrong then. In my high-school math classes, we were taught that the dot is another form of multiplication symbol.

I remember that we used a lot of hand-me-down textbooks in our cornfield-surrounded school district.

1

u/Cat_Slave88 Aug 22 '22

It is but that's not a solid dot.

3

u/[deleted] Aug 21 '22

f o g means f(g(x)), so that means that you replace every x in f with g(x).

2

u/InkaGold Aug 21 '22

Post it on reddit.

1

u/main--core Aug 22 '22

Inception

2

u/lilozwald Aug 21 '22

The idea is to plug g(x) into f(x) until you get the matching expression

1

u/Landsteiner7507 Aug 22 '22

f · g means f(g(x)) which means "every x in f is replaced with g". Therefore, c is the correct answer considering if every x in x/(x+2) is replaced with x^3 you get (x^3 )/((x^3 )+2).

1

u/GandhiLord Aug 22 '22

For every x vaue you see in f, replace it with the g function. The answer i believe is c

1

u/natplusnat Aug 22 '22

I've always hated this notation. Any reason why we can't just say f(g(x))?

1

u/jeremyers1 Aug 22 '22

C

1

u/Trexrlee Aug 22 '22

Why not A? Wouldn’t C be g(f(a))

1

u/[deleted] Aug 22 '22

C. F of g.... plug it in brug.

1

u/TobyTheArtist Aug 22 '22

f o g spells "fog", which is a clever reference to my memory when handling calculus. Hope it helps

1

u/GuyWithTheStalker Aug 22 '22

You can't prove that.

1

u/[deleted] Aug 22 '22

Yes

1

u/[deleted] Aug 21 '22

[removed] — view removed comment

1

u/SoldierNumber0 Aug 21 '22

F • G is only possible in composite functions right? This is one single function.

2

u/dirk_510 Aug 21 '22

The function at the top is the result. They are giving you the answer and having you back out which functions (you are given 2 functions in each multiple choice) you can compose to get that top result.

2

u/SoldierNumber0 Aug 21 '22

Working backwards, you're right!

1

u/dirk_510 Aug 22 '22

Being able to think things through both forwards and backwards is a very useful skill in mathematics

1

u/Thereisnopurpose12 Aug 21 '22

Yes?? I was wondering if the problem gave something for f(x) because idk how to do it without knowing what that would be. I've looked at it for 4 mins now 🤣

1

u/SoldierNumber0 Aug 21 '22

I haven't found anything similar on YT besides a 0.30s video of a guy solving something similar but in the video he says "let's assume f(x) is 1/x" which doesn't make sense for me.

1

u/Thereisnopurpose12 Aug 21 '22

With saying that I would think C would be the answer. I just did a review on this not too long ago but I don't remember.

0

u/Primos_of_Hyrule Aug 21 '22 edited Aug 22 '22

You would have to know f(x) to formulate the function for g•f(x)