# Math Help - Compositions of functions

1. ## Compositions of functions

How to finde the following:
x, if f(x) = 0
h(6) if h(x) = square root(18 - 4x)

2. Originally Posted by Snowboarder
How to finde the following:
x, if f(x) = 0 Mr F says: This makes no sense. What is the rule for f(x)?

h(6) if h(x) = square root(18 - 4x) Mr F says: Substitute x = 6 into the given rule. You get an answer that's not real.
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3. Originally Posted by Snowboarder
How to finde the following:
x, if f(x) = 0
h(6) if h(x) = square root(18 - 4x)
Let's assume $f(x) = h(x)$

$h(x) = \sqrt{18-4x}$

$h(6) = \sqrt{18-4(6)} \Rightarrow \sqrt{-24} = 2i\sqrt{6}$

$h(x) = 0$

$\sqrt{18-4x} = 0$

$18-4x = 0$

$4x=18$

$x=\frac{9}{2}$