To find f(3z) for the function f(x) = x^2 + 5, substitute 3z for x in the definition. This results in f(3z) = (3z)^2 + 5, which simplifies to 9z^2 + 5. The discussion emphasizes the importance of correctly substituting and simplifying the input. Additionally, participants are reminded to keep questions organized by starting new threads for new topics. The final result is f(3z) = 9z^2 + 5.
Everywhere in the definition of $f(x)$, where you see an $x$, replace it with a $3z$, and then simplify as needed. What do you find?
#3
zolton5971
25
0
f(3z)=5
I'm not sure I not very good at this.
#4
MarkFL
Gold Member
MHB
13,284
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We are given the definition:
$$f(x)=x^2+5$$
Notice that in the definition, we are told to take the input, square it, and then add 5. So, say the input is $4u$, then we need to square that, which is $(4u)^2$, and then add 5, so that we have $(4u)^2+5$. Hence:
$$f(4u)=(4u)^2+5=4^2u^2+5=16u^2+5$$
Can you now find $f(3z)$?
#5
zolton5971
25
0
f(3z)=3x^2+5= 9z^2+5 is that close?
#6
MarkFL
Gold Member
MHB
13,284
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zolton5971 said:
f(3z)=3x^2+5= 9z^2+5 is that close?
You have the right end result, but what you want to write is:
$$f(3z)=(3z)^2+5=9z^2+5$$
#7
zolton5971
25
0
Ok thanks!
#8
MarkFL
Gold Member
MHB
13,284
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I have again moved a new question of yours into a new thread. Please don't tag a new question onto an existing thread, as this can cause threads to become convoluted and hard to follow. Also, your new question will be seen by more people if you begin a new thread for it. :D