$Find k, if f (x) = x + 1 and f o f (x) = 9.$

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Solution

$Given, f (x) = x + 1$
$f o f (x) = f {f (x)}$
$= f {x + 1} = x + 2 (1 m a r k)$
$Given, f o f (x) = 9 ∴ x + 2 = 9 \Rightarrow x = 7$ (1 mark)

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