work needing to be checked thus far:
f(x)=x^3 and g(x) =5+4x Find (fog)(X)
my work:
(fog)(x) = f(g(x))
=f(5+4x)^3
im not sure if that's right to start out with ...

Question

work needing to be checked thus far:
f(x)=x^3 and g(x) =5+4x Find (fog)(X)
my work:
(fog)(x) = f(g(x))
=f(5+4x)^3
im not sure if that's right to start out with ...

anonymous · Answer

Its right.

bibby · Answer

(fog)(x) = f(g(x)) is correct. that's how the composite function works

you replace the x in f(x) with (5+4x)

anonymous · Answer

okay I wasn't sure if I placed the ^3 in the correct place

anonymous · Answer

ty is my answer  64x^3 + 125?

bibby · Answer

I dunno is it? :)

Post your work as I'm gettin ga different answer

anonymous · Answer

yes! =)

bibby · Answer

$$64x^3+240x^2+300x+15$$

anonymous · Answer

(fog)(x)=f(5+4x)^3
=125 +64x^3

anonymous · Answer

the one u got is very not right lol

bibby · Answer

I checked wolfram alpha .com. I'm pretty sure I'm right

anonymous · Answer

that's not what any of my answers look like

bibby · Answer

I actually multiplied out (5+4x)(5+4x)(5+4x) http://www.wolframalpha.com/input/?i=%285%2B4x%29%5E3 I'm almost positive I'm right and you can call someone else to check. Either way (5+4x)^3 should be fine as an answer

anonymous · Answer

thats what one of my answers look like . oh sorry I didn't even think about going as far as you did ... your good!

bibby · Answer

Sorry if I come across as a jerk. I'm glad I could help in any sort of manner