Find the roots exactly: Solve 2x^2 − 11x + 15 = 0.

Difficulty: Easy

Correct Answer: 3 and 5/2

Explanation:


Introduction / Context:
Factoring is often the fastest way to solve a quadratic with integer coefficients if a suitable factor pair exists. Here the numbers factor cleanly, yielding rational roots without the quadratic formula.


Given Data / Assumptions:

  • Equation: 2x^2 − 11x + 15 = 0
  • Look for factorization into (2x − m)(x − n) with mn = 15 and 2n + m = 11.


Concept / Approach:
We seek integers m, n such that 2x^2 − 11x + 15 = (2x − 5)(x − 3). Then set each factor to zero to get the roots. This is quicker than the quadratic formula and equally valid.


Step-by-Step Solution:

2x^2 − 11x + 15 = (2x − 5)(x − 3)Set factors to zero: 2x − 5 = 0 ⇒ x = 5/2; x − 3 = 0 ⇒ x = 3


Verification / Alternative check:
Expand (2x − 5)(x − 3) = 2x^2 − 6x − 5x + 15 = 2x^2 − 11x + 15, confirming correctness.


Why Other Options Are Wrong:

  • Other sign variants do not satisfy the original equation when substituted.


Common Pitfalls:
Misassigning signs to factor pairs of 15, or mixing the coefficient 2 into the wrong factor, leading to cross-term errors.


Final Answer:
3 and 5/2

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