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# C3 Functions Help Please watch

1. the functions f and g are defined by f(x) = 3x-5 and g(x) = 3-2x

evaluate
c) fg(4)

d) the composite function is defined by h=gf. find h(x)

my working out:

c) sub x with 4 and times f and g together?

d) times g and f together?

ahhhh :/
2. For C, sub x with 4 in g(x) then sub x for your answer from g(x) into f(x)
3. think of it as f(g(4)) rather than fg(4).

So evaluate g(4) then use that answer as the x when evaluating f.

Do the same for d.
4. For D, sub in f(x) as x in g(x)

so

3 - 2(3x - 5)
5. (Original post by Jabba1024)
For D, sub in f(x) as x in g(x)

so

3 - 2(3x - 5)
thank you so much for your help!

another quick question

f(x) = 5x + 4

find f^-1(x) and verify that the composite function f f ^-1(x) = x

for the first part do you just sub -x in? for the second part have nooo idea
6. (Original post by boomboompow.)
f(x) = 5x + 4

find f^-1(x) and verify that the composite function f f ^-1(x) = x

for the first part do you just sub -x in? for the second part have nooo idea
A little trick: take everything "one step back."
So make , and every .

You'll then get:

And then, for the first part, simply re-arrange this to make the subject!

It's probably best to post again once you've cracked the first part, before tackling the 2nd straight after ~

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