Question 11

Let $$f(x)=\log_{e}x$$ and $$g(x)=\frac{x^{4}-2x^{3}+3x^{2}-2x+2}{2x^{2}-2x+1}$$. Then the domain of $$f \circ g$$ is

Let $$f(x) = \ln x$$ and $$g(x) = \frac{x^4 - 2x^3 + 3x^2 - 2x + 2}{2x^2 - 2x + 1}$$. We need to find the domain of $$f \circ g$$.

$$f(g(x)) = \ln(g(x))$$ is defined when $$g(x) > 0$$ and $$g(x)$$ itself is defined (denominator $$\neq 0$$).

$$2x^2 - 2x + 1 = 0$$ has discriminant $$4 - 8 = -4 < 0$$.

Since the leading coefficient is positive and discriminant is negative, $$2x^2 - 2x + 1 > 0$$ for all real $$x$$. So $$g(x)$$ is defined for all $$x \in \mathbb{R}$$.

We perform polynomial division of the numerator by the denominator:

$$x^4 - 2x^3 + 3x^2 - 2x + 2 = (2x^2 - 2x + 1) \cdot q(x) + r(x)$$

Dividing: $$\frac{x^4 - 2x^3 + 3x^2 - 2x + 2}{2x^2 - 2x + 1}$$

$$= \frac{1}{2}x^2 - \frac{1}{2}x + 1 + \frac{-\frac{1}{2}x + 1}{2x^2 - 2x + 1}$$

Alternatively, note that the numerator can be written as:

$$x^4 - 2x^3 + 3x^2 - 2x + 2 = (x^2 - x)^2 + 2(x^2 - x) + 2 = (x^2-x+1)^2 + 1$$

Let us verify: $$(x^2-x+1)^2 = x^4 - 2x^3 + 3x^2 - 2x + 1$$. Adding 1 gives $$x^4 - 2x^3 + 3x^2 - 2x + 2$$. Confirmed.

So the numerator equals $$(x^2 - x + 1)^2 + 1 \geq 1 > 0$$ for all real $$x$$.

Since both numerator and denominator are strictly positive for all $$x \in \mathbb{R}$$, we have $$g(x) > 0$$ for all $$x$$.

The domain of $$f \circ g$$ is all of $$\mathbb{R}$$.

The correct answer is Option 4: $$\mathbb{R}$$.

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