在不使用计算器的情况下,解不等式 (x2−2x+4)(x−3)(x+2)≥0.\frac{(x^2 - 2x + 4)(x - 3)}{(x + 2)} \ge 0. 由此解不等式 (x2−2∣x∣+4)(∣x∣−3)(∣x∣+2)≥0.\frac{(x^2 - 2|x| + 4)(|x| - 3)}{(|x| + 2)} \ge 0.

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完整解法

3(i)

1. Show that the quadratic factor in the numerator is always positive.

By completing the square for x2−2x+4x^2 - 2x + 4:
x2−2x+4=(x−1)2−12+4x^2 - 2x + 4 = (x - 1)^2 - 1^2 + 4
x2−2x+4=(x−1)2+3x^2 - 2x + 4 = (x - 1)^2 + 3
Since (x−1)2≥0(x - 1)^2 \ge 0 for all real xx, it follows that (x−1)2+3≥3>0(x - 1)^2 + 3 \ge 3 > 0.
Thus, x2−2x+4x^2 - 2x + 4 is always strictly positive.

2. Simplify the inequality by removing the positive factor.

Since x2−2x+4>0x^2 - 2x + 4 > 0 for all real xx, dividing both sides of the inequality by this expression will not change the inequality sign.
x−3x+2≥0\frac{x - 3}{x + 2} \ge 0

3. Convert the rational inequality to a polynomial inequality.

Multiply both sides by (x+2)2(x + 2)^2. Since (x+2)2>0(x + 2)^2 > 0 for x≠−2x \neq -2, the inequality sign remains unchanged:
x−3x+2×(x+2)2≥0×(x+2)2\frac{x - 3}{x + 2} \times (x + 2)^2 \ge 0 \times (x + 2)^2
(x−3)(x+2)≥0(x - 3)(x + 2) \ge 0
Note that x≠−2x \neq -2 to avoid a zero denominator in the original rational expression.

4. Solve the resulting quadratic inequality and deduce the final range.

The critical values for (x−3)(x+2)≥0(x - 3)(x + 2) \ge 0 are x=−2x = -2 and x=3x = 3.
Because it is a '≥0\ge 0' inequality with a positive x2x^2 coefficient, the solution lies outside the roots:
x≤−2 or x≥3x \le -2 \text{ or } x \ge 3
However, because x≠−2x \neq -2 (undefined denominator), we reject x=−2x = -2.
Therefore, the solution is:
x<−2 or x≥3x < -2 \text{ or } x \ge 3

答案

x<−2 or x≥3x < -2 \text{ or } x \ge 3

3(ii)

1. Concisely solve the inequality from part (i) to find the base solution range.

For the quadratic factor, x2−2x+4=(x−1)2+3>0x^2 - 2x + 4 = (x - 1)^2 + 3 > 0 for all real xx.
Dividing both sides by this strictly positive factor, the inequality in (i) simplifies to:
x−3x+2≥0\frac{x - 3}{x + 2} \ge 0
By testing intervals around the critical values x=−2x = -2 (where the expression is undefined) and x=3x = 3 (where it is zero), the solution to (i) is:
x<−2orx≥3x < -2 \quad \text{or} \quad x \ge 3

2. Substitute $|x|$ for $x$ in the base solution, recognising that $x^2 = |x|^2$.

The inequality in (ii) can be rewritten as:
(∣x∣2−2∣x∣+4)(∣x∣−3)∣x∣+2≥0\frac{(|x|^2 - 2|x| + 4)(|x| - 3)}{|x| + 2} \ge 0
This is the exact same inequality as in (i), but with xx replaced by ∣x∣|x|. Using the result from (i), we substitute xx with ∣x∣|x| to get:
∣x∣<−2or∣x∣≥3|x| < -2 \quad \text{or} \quad |x| \ge 3

3. Solve the resulting modulus inequalities for $x$.

Since the absolute value of any real number is non-negative (∣x∣≥0|x| \ge 0), the inequality ∣x∣<−2|x| < -2 has no real solution.
For the remaining inequality:
∣x∣≥3|x| \ge 3
This gives the solution:
x≤−3orx≥3x \le -3 \quad \text{or} \quad x \ge 3

答案

x≤−3 or x≥3x \le -3 \text{ or } x \ge 3

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