Question:medium

The quadratic equation whose roots are \(\frac{1}{3+\sqrt{2}}\) and \(\frac{1}{3-\sqrt{2}}\), will be:

Show Hint

Rationalize denominators before finding sum and product of roots.
Updated On: May 21, 2026
  • \(7x^2 - 6x + 1 = 0\)
  • \(6x^2 - 7x + 1 = 0\)
  • \(x^2 - 6x + 7 = 0\)
  • \(x^2 - 7x + 6 = 0\)
Show Solution

The Correct Option is A

Solution and Explanation

To solve this problem, we need to find the quadratic equation given the roots \(\frac{1}{3+\sqrt{2}}\) and \(\frac{1}{3-\sqrt{2}}\). Let's begin by simplifying these roots:

  1. Rationalize the roots:
    \(x_1 = \frac{1}{3+\sqrt{2}} = \frac{1}{3+\sqrt{2}} \times \frac{3-\sqrt{2}}{3-\sqrt{2}} = \frac{3-\sqrt{2}}{9-2} = \frac{3-\sqrt{2}}{7}\)
    \(x_2 = \frac{1}{3-\sqrt{2}} = \frac{1}{3-\sqrt{2}} \times \frac{3+\sqrt{2}}{3+\sqrt{2}} = \frac{3+\sqrt{2}}{9-2} = \frac{3+\sqrt{2}}{7}\)
  2. Sum and product of roots:
    • Sum of roots \((s)\) is given by:
      \(s = x_1 + x_2 = \frac{3-\sqrt{2}}{7} + \frac{3+\sqrt{2}}{7} = \frac{6}{7}\)
    • Product of roots \((p)\) is given by:
      \(p = x_1 \cdot x_2 = \left(\frac{3-\sqrt{2}}{7}\right)\left(\frac{3+\sqrt{2}}{7}\right) = \frac{9 - 2}{49} = \frac{7}{49} = \frac{1}{7}\)
  3. Using the formula for a quadratic equation with roots \(x_1\) and \(x_2\):
    \(x^2 - sx + p = 0\)
  4. Substitute the sum and product of roots into the equation:
    \(x^2 - \left(\frac{6}{7}\right)x + \frac{1}{7} = 0\)
  5. Clear the fractions by multiplying the entire equation by 7 to obtain integer coefficients: \(7x^2 - 6x + 1 = 0\)

Thus, the quadratic equation whose roots are \(\frac{1}{3+\sqrt{2}}\) and \(\frac{1}{3-\sqrt{2}}\) is \(7x^2 - 6x + 1 = 0\).

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