Question

Difficulty: MediumLinear and Quadratic Inequalities

Which of the following ranges of xx satisfies the quadratic inequality 2x27x+3<02x^2 - 7x + 3 < 0?

  1. 12<x<3\frac{1}{2} < x < 3Answer
  2. B
    x<12 or x>3x < \frac{1}{2} \text{ or } x > 3
  3. C
    3<x<12-3 < x < -\frac{1}{2}
  4. D
    x<3 or x>12x < -3 \text{ or } x > -\frac{1}{2}

Answer

12<x<3\frac{1}{2} < x < 3
Factorizing 2x27x+3<02x^2 - 7x + 3 < 0 gives (2x1)(x3)<0(2x - 1)(x - 3) < 0. The roots of the quadratic equation (2x1)(x3)=0(2x - 1)(x - 3) = 0 are x=12x = \frac{1}{2} and x=3x = 3. Because the coefficient of x2x^2 is positive, the quadratic curve opens upwards and is strictly negative between the two roots. Therefore, the inequality is satisfied when 12<x<3\frac{1}{2} < x < 3.

Step-by-Step Solution

1
Factorize the quadratic expression
2x27x+3=(2x1)(x3)2x^2 - 7x + 3 = (2x - 1)(x - 3)
Factorization allows us to find the critical values of the inequality.
2
Determine the critical values by setting the factored expression to zero
x=12x = \frac{1}{2} and x=3x = 3
These points mark the boundary values where the quadratic expression changes sign.
3
Test intervals or apply sign analysis for strict inequality <0< 0
The product (2x1)(x3)(2x - 1)(x - 3) is negative for 12<x<3\frac{1}{2} < x < 3
Since the leading coefficient is positive (2>02 > 0), the parabola opens upwards and takes negative values strictly between its real roots.

Key Concept

Solving Quadratic Inequalities by Factorization and Interval Sign Analysis
Estimated Time:1m 15s
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