What is the value of k if the quadratic equation x^2 + kx + 9 = 0 has roots 3 an

Practice Questions

Q1
What is the value of k if the quadratic equation x^2 + kx + 9 = 0 has roots 3 and -3? (2022)
  1. 0
  2. 6
  3. 9
  4. 12

Questions & Step-by-Step Solutions

What is the value of k if the quadratic equation x^2 + kx + 9 = 0 has roots 3 and -3? (2022)
  • Step 1: Identify the given quadratic equation, which is x^2 + kx + 9 = 0.
  • Step 2: Recognize that the roots of the equation are given as 3 and -3.
  • Step 3: Use Vieta's formulas, which tell us that the sum of the roots (3 + -3) equals -k.
  • Step 4: Calculate the sum of the roots: 3 + (-3) = 0.
  • Step 5: Set the sum equal to -k: 0 = -k.
  • Step 6: Solve for k: k = 0.
  • Step 7: Now, use Vieta's formulas again to find the product of the roots, which is 3 * -3 = -9.
  • Step 8: According to Vieta's formulas, the product of the roots is also equal to 9, which confirms the equation.
  • Step 9: Since the product of the roots is correct, we can conclude that k = 0.
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