Compute the absolute difference between the two real roots of the quadratic equation 2x^2 − 11x + 5 = 0.

Difficulty: Easy

Correct Answer: 4.5

Explanation:

Introduction / Context: The distance between the roots of a quadratic can be computed without solving for each root explicitly by using the identity |α − β| = sqrt((α + β)^2 − 4αβ). This leverages sum and product of roots from coefficients.

Given Data / Assumptions:

  • Equation: 2x^2 − 11x + 5 = 0.
  • Real roots exist (discriminant positive).

Concept / Approach: For ax^2 + bx + c = 0, α + β = −b/a and αβ = c/a. Then |α − β| = sqrt((α + β)^2 − 4αβ). This avoids computing α and β separately.

Step-by-Step Solution:

a = 2, b = −11, c = 5.α + β = −b/a = 11/2.αβ = c/a = 5/2.|α − β| = sqrt((11/2)^2 − 4*(5/2)) = sqrt(121/4 − 10) = sqrt(81/4) = 9/2 = 4.5.

Verification / Alternative check: Solving explicitly via quadratic formula also yields roots whose difference is 4.5; the identity is quicker and exact.

Why Other Options Are Wrong: They correspond to common arithmetic slips (e.g., missing the division by a or miscomputing the constant term).

Common Pitfalls: Using sqrt(b^2 − 4ac)/a directly and forgetting to divide by |a|, which leads to the same value but often mishandled.

Final Answer: 4.5

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