函数 的定义为
- (i)
解释为什么函数 不存在。
- (ii)
用代数方法求使 单调递减的 的取值集合。
- (iii)
在问题的其余部分中, 的定义域进一步限制为 。
函数 的定义为
求 的表达式,并由此或用其他方法求 的值。
它不会直接告诉你答案,而是问你卡在哪一步看看 AI 是怎么陪你一步步弄懂这道题的
完整解法
9(i)
1. Evaluate the function at two distinct points to find a counterexample for the one-to-one property.
Let ,
Let ,
2. Conclude that the function is not one-to-one, meaning its inverse does not exist.
Since for , the function is not a one-to-one function.
Therefore, the inverse function does not exist.
Since , the function is not one-to-one. Therefore, does not exist.
9(ii)
1. Find the first derivative of $\text{f}(x)$.
Rewrite using a negative index:
Differentiate with respect to using the chain rule:
2. Set up the inequality for a decreasing function.
For the function to be decreasing, its gradient must be negative, so .
3. Solve the rational inequality.
The denominator is a perfect square, meaning for all valid in the domain (where and ).
Therefore, the sign of the derivative depends entirely on the numerator. For the fraction to be negative, we must have:
4. Combine with the domain restrictions to state the final set of values.
The given domain restricts and .
The condition already excludes . However, is greater than and thus falls within this region, so it must still be explicitly excluded.
The set of values is therefore .
(Note: is also acceptable depending on the rigorous definition of decreasing vs strictly decreasing)
9(iii)
1. Find an expression for $\text{gf}(x)$ by substituting $\text{f}(x)$ into $\text{g}(x)$.
2. Set up an equation to evaluate the inverse function at $\frac{1}{4}$ and solve the resulting quadratic equation.
Let .
3. Determine the valid root by considering the domain restriction.
Since the domain of is restricted to , the domain of is also .
We reject .
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