已知 且 ,利用代数方法求解不等式 由此求出满足 的 的取值集合。
- (i)
已知 且 ,利用代数方法求解不等式
- (ii)
由此求出满足 的 的取值集合。
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完整解法
3(i)
1. Rearrange the inequality to have 0 on one side and express it as a single algebraic fraction.
2. Analyse the sign of the numerator.
Consider the numerator :
Completing the square, we get:
Since for all real , it follows that for all real .
(Alternatively, the discriminant , and since the coefficient of is positive, the quadratic is strictly positive.)
3. Deduce the required inequality for the denominator and solve it.
Since the numerator is always strictly positive, for the whole fraction to be , the denominator must be strictly negative (note that the denominator cannot be equal to as division by zero is undefined).
Multiplying both sides by reverses the inequality sign:
Given that , the critical values are and , and they are ordered . Solving this quadratic inequality yields:
3(ii)
1. Concisely solve the inequality from part (i) to establish the base result.
\n\n\nSince for all real , we require the denominator to be negative:\n\nGiven , the solution to part (i) is .
2. Apply the substitution $x \to |x|$ to the result of part (i).
Comparing the target inequality with the one in part (i), we can substitute with in the solution set:\n
3. Solve the resulting modulus inequalities to find the final range of $x$.
For :\n\nFor , since we are given :\n\nCombining these disjoint intervals, the set of values of is:\n
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