$Find k, if f (k) = 2 k - 1 and f o f (k) = 5.$

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Solution

The correct option is B 2
$Given, f (k) = 2 k - 1$
$f o f (k) = f {f (k)}$
$= f {2 k - 1} = 2 (2 k - 1) - 1 = 4 k - 2 - 1 = 4 k - 3$
$Given, f o f (k) = 5 ∴ 4 k - 3 = 5 \Rightarrow 4 k = 8 \Rightarrow k = 2$

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