解答本题时请勿使用计算器。

  1. 解不等式

    6x2+2x−32x−1≥2(x+1).\frac{6x^2 + 2x - 3}{2x - 1} \ge 2(x + 1).

  2. 由此求解 6x2+2∣x∣−32∣x∣−1≥2(∣x∣+1)\frac{6x^2 + 2|x| - 3}{2|x| - 1} \ge 2(|x| + 1)。

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完整解法

3[0]

1. Rearrange the inequality to have zero on one side and combine the terms into a single algebraic fraction.

6x2+2x−32x−1−2(x+1)≥0\frac{6x^2 + 2x - 3}{2x - 1} - 2(x + 1) \ge 0

6x2+2x−3−2(x+1)(2x−1)2x−1≥0\frac{6x^2 + 2x - 3 - 2(x + 1)(2x - 1)}{2x - 1} \ge 0

2. Expand and simplify the numerator.

2(x+1)(2x−1)=2(2x2+x−1)=4x2+2x−22(x + 1)(2x - 1) = 2(2x^2 + x - 1) = 4x^2 + 2x - 2

6x2+2x−3−(4x2+2x−2)2x−1≥0\frac{6x^2 + 2x - 3 - (4x^2 + 2x - 2)}{2x - 1} \ge 0

2x2−12x−1≥0\frac{2x^2 - 1}{2x - 1} \ge 0

3. Identify the critical values by setting the numerator and denominator to zero.

Numerator: 2x2−1=0  ⟹  x2=12  ⟹  x=±12=±222x^2 - 1 = 0 \implies x^2 = \frac{1}{2} \implies x = \pm\frac{1}{\sqrt{2}} = \pm\frac{\sqrt{2}}{2}

Denominator: 2x−1=0  ⟹  x=122x - 1 = 0 \implies x = \frac{1}{2}

4. Use a sign test to determine the intervals satisfying the inequality.

The critical values in ascending order are −22-\frac{\sqrt{2}}{2}, 12\frac{1}{2}, and 22\frac{\sqrt{2}}{2} (since 22≈0.707>0.5\frac{\sqrt{2}}{2} \approx 0.707 > 0.5).

Testing the sign of 2x2−12x−1\frac{2x^2 - 1}{2x - 1} in each interval:

  • x<−22x < -\frac{\sqrt{2}}{2} (e.g., x=−1x = -1): 2−1−2−1=−13<0\frac{2 - 1}{-2 - 1} = -\frac{1}{3} < 0
  • −22<x<12-\frac{\sqrt{2}}{2} < x < \frac{1}{2} (e.g., x=0x = 0): −1−1=1>0\frac{-1}{-1} = 1 > 0
  • 12<x<22\frac{1}{2} < x < \frac{\sqrt{2}}{2} (e.g., x=0.6x = 0.6): 2(0.36)−11.2−1=−0.280.2<0\frac{2(0.36) - 1}{1.2 - 1} = \frac{-0.28}{0.2} < 0
  • x>22x > \frac{\sqrt{2}}{2} (e.g., x=1x = 1): 2−12−1=1>0\frac{2 - 1}{2 - 1} = 1 > 0

The fraction must be ≥0\ge 0. The roots of the numerator are included, but the root of the denominator (x=12x = \frac{1}{2}) must be excluded to avoid division by zero.

Thus, −22≤x<12-\frac{\sqrt{2}}{2} \le x < \frac{1}{2} or x≥22x \ge \frac{\sqrt{2}}{2}.

答案

−22≤x<12 or x≥22-\frac{\sqrt{2}}{2} \le x < \frac{1}{2} \text{ or } x \ge \frac{\sqrt{2}}{2}

3[1]

1. Solve the inequality from part [0] to establish the foundation for substitution.

6x2+2x−32x−1−2(x+1)≥0\frac{6x^2 + 2x - 3}{2x - 1} - 2(x + 1) \ge 0
6x2+2x−3−2(2x2+x−1)2x−1≥0\frac{6x^2 + 2x - 3 - 2(2x^2 + x - 1)}{2x - 1} \ge 0
2x2−12x−1≥0\frac{2x^2 - 1}{2x - 1} \ge 0
Finding the critical values, we set the numerator and denominator to zero:
2x2−1=0  ⟹  x=±122x^2 - 1 = 0 \implies x = \pm \frac{1}{\sqrt{2}}
2x−1=0  ⟹  x=122x - 1 = 0 \implies x = \frac{1}{2}
Analysing the signs of the expression across these intervals gives the solution for part [0]:
−12≤x<12orx≥12-\frac{1}{\sqrt{2}} \le x < \frac{1}{2} \quad \text{or} \quad x \ge \frac{1}{\sqrt{2}}

2. Substitute $x$ with $|x|$ to relate the target inequality to the previous part.

Since x2=∣x∣2x^2 = |x|^2, the target inequality is algebraically identical to the one in part [0] but with ∣x∣|x| replacing xx:
6∣x∣2+2∣x∣−32∣x∣−1≥2(∣x∣+1)\frac{6|x|^2 + 2|x| - 3}{2|x| - 1} \ge 2(|x| + 1)
Substituting ∣x∣|x| into the solution from part [0]:
−12≤∣x∣<12or∣x∣≥12-\frac{1}{\sqrt{2}} \le |x| < \frac{1}{2} \quad \text{or} \quad |x| \ge \frac{1}{\sqrt{2}}

3. Solve the first inequality involving the modulus.

For the range −12≤∣x∣<12-\frac{1}{\sqrt{2}} \le |x| < \frac{1}{2}, we note that ∣x∣≥0|x| \ge 0 is naturally true for all real values of xx. Thus, we only need to solve ∣x∣<12|x| < \frac{1}{2}:
−12<x<12-\frac{1}{2} < x < \frac{1}{2}

4. Solve the second inequality involving the modulus and combine the valid ranges.

For the range ∣x∣≥12|x| \ge \frac{1}{\sqrt{2}}, expanding the modulus condition gives:
x≤−12orx≥12x \le -\frac{1}{\sqrt{2}} \quad \text{or} \quad x \ge \frac{1}{\sqrt{2}}
Combining all the separate valid ranges of xx gives the final continuous solution set.

答案

x≤−12x \le -\frac{1}{\sqrt{2}} or −12<x<12-\frac{1}{2} < x < \frac{1}{2} or x≥12x \ge \frac{1}{\sqrt{2}}

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