Find the exact roots: Solve √7 x^2 − 6x − 13√7 = 0 and identify the correct ordered pair of roots.

Difficulty: Easy

Correct Answer: −√7 , 13√7 / 7

Explanation:


Introduction / Context:
This quadratic uses an irrational leading coefficient a = √7. We can still apply the quadratic formula to obtain exact roots in terms of √7 and simplify carefully.

Given Data / Assumptions:

  • Equation: √7 x^2 − 6x − 13√7 = 0.
  • a = √7, b = −6, c = −13√7.


Concept / Approach:
Use x = [−b ± √(b^2 − 4ac)] / (2a). Compute the discriminant first; simplify square roots of perfect squares when they appear.

Step-by-Step Solution:

Δ = b^2 − 4ac = (−6)^2 − 4*(√7)*(−13√7) = 36 + 4*13*7 = 36 + 364 = 400.√Δ = √400 = 20.x = [6 ± 20] / (2√7).Case 1: x = (6 + 20)/(2√7) = 26/(2√7) = 13/√7 = 13√7/7.Case 2: x = (6 − 20)/(2√7) = −14/(2√7) = −7/√7 = −√7.


Verification / Alternative check:
Substitute x = −√7: a x^2 = √7*(7) = 7√7; b x = −6*(−√7) = 6√7; c = −13√7. Sum = (7 + 6 − 13)√7 = 0. Likewise, x = 13√7/7 also satisfies the equation.


Why Other Options Are Wrong:

  • Options with incorrect sign ordering or both negatives do not satisfy the original equation upon substitution.


Common Pitfalls:
Dropping √7 during simplification or mishandling rationalization. Keep terms symbolic and only rationalize if needed.


Final Answer:

−√7 , 13√7 / 7

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