Digital SAT Math

SAT Math: Find the Sum and Product of the Roots of 5x² - 15x - 7 = 0 (Vieta's Formulas)

2026-08-23 5 min read
• Direct Answer / Key Takeaway

By Vieta's formulas, sum of roots = -b/a = -(-15)/5 = 3.

Exact Question Text

What is the sum of the solutions to the quadratic equation 5x^2 - 15x - 7 = 0?

1. Step-by-Step Formal Solution

  1. In ax^2 + bx + c = 0, sum of roots = -b/a.
  2. a = 5, b = -15 => -(-15)/5 = 15/5 = 3.

2. Fast Desmos / Calculator Shortcut

Type solutions in Desmos using quadratic formula and add them: sum equals exactly 3.


3. Distractor Trap Analysis

  • Trap A (Sign Flip): Forgetting to reverse inequality or dropping negative sign.
  • Trap B (Partial Evaluation): Solving for intermediate variable and stopping early.
  • Trap C (Extreme Assumption): Over-inferring beyond textual evidence.
  • Option Correct: Accurately satisfies all algebraic and logical constraints.

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