Question
If f(x) = sin2x and the composite function $\text{g(f(x))} = |\sin\text{x}|,$ then g(x) is equal to:

  1. $\sqrt{\text{x}-1}$

  2. $\sqrt{\text{x}}$

  3. $\sqrt{\text{x}+1}$

  4. $-\sqrt{\text{x}}$

Answer

  1. $\sqrt{\text{x}}$

Solution:

Given that $\text{f(x)}=\sin^2\text{x}$ and the composite function $\text{g(f(x))}=|\sin\text{x}|$

We will do it using trial and error method.

If we take $\text{g(x)}=-\sqrt{\text{x}}$ and $\text{f(x)}=\sin^2\text{x}$

​​​​​​​$\text{g(f(x))}=\text{g}(\sin^2\text{x})$

$=-\sin\text{x}$

Which contradicts to the $\text{g(f(x))}=|\sin\text{x}|$

Hence, we take $\text{g(x)}=\sqrt{\text{x}}$

$\text{g(f(x))}=\text{g}(\sin^2\text{x})$

$=\sqrt{\sin^2\text{x}}=|\sin\text{x}|$

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