Find fog(2) when f(x)=-x^2 + 4X and g(x) = 2 ^x -1

Question

anonymous · Answer

Put g(x) for ALL x's in f(x)

anonymous · Answer

thanks ! can you help me get a numerical answer i got 21 and I'm unsure if it is correct

anonymous · Answer

sure, can you confirm the that g(x)= 2^x-1

anonymous · Answer

You get 3 but then when i plug in for f(x) i get 21 but someone else told me it was three so i am unsure if i am right or if they are right

anonymous · Answer

Just type the question again

anonymous · Answer

Find fog(2) when f(x)=-x^2 + 4X and g(x) = 2 ^x -1, im trying to figure out if the final answer is 21

anonymous · Answer

$$is g(x)=2^{x} - 1$$

anonymous · Answer

what you have typed is pretty confusing

anonymous · Answer

yes it is that formula you wrote but it is g(x)

anonymous · Answer

$g(2)=2^2-1=3$ find $f(3)$

anonymous · Answer

thanks, i got that part now i need to know if the final answer is 21

anonymous · Answer

since $f(x)=-x^2 + 4x$ just do f(3) which means you plug in 3 for all the x's like so:$$f(3)=-(3)^2+4(3)~~~~\implies~~~~f(3)=-9+12~~~~\implies~~~~f(3)=3$$ 
i hope it makes sense now! :) @wonderstruck

anonymous · Answer

yayyyy ! im so glad! lol thanks so much !!  :DDD

anonymous · Answer

youre welcome! :D