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Let \(\alpha\) and \(\beta\) be the roots of the quadratic equation \(x^2 - 2bx + c^2 = 0\) where b, c are positive real numbers. Let A be the arithmetic mean of \(\alpha\) and \(\beta\); and G be the geometric mean of \(\alpha\) and \(\beta\). What are the roots of the quadratic equation \(x^2 - (b+c)x + bc = 0\) ?

This question was previously asked in
NDA 2 2026 GAT Question Paper (13-Sep-2026)
The correct answer is
A, G

Finding Roots of the First Quadratic Equation

Given the quadratic equation: \(x^2 - 2bx + c^2 = 0\)

Let the roots be \(\alpha\) and \(\beta\). Using Vieta's formulas:

  • Sum of roots: \(\alpha + \beta = -(\frac{-2b}{1}) = 2b\)
  • Product of roots: \(\alpha \beta = \frac{c^2}{1} = c^2\)

Calculating Arithmetic Mean (A) and Geometric Mean (G)

The arithmetic mean (A) of \(\alpha\) and \(\beta\) is: \(A = \frac{\alpha + \beta}{2} = \frac{2b}{2} = b\)

The geometric mean (G) of \(\alpha\) and \(\beta\) is: \(G = \sqrt{\alpha \beta}\) Since \(\alpha \beta = c^2\) and \(c\) is a positive real number, \(G = \sqrt{c^2} = c\).

Finding Roots of the Second Quadratic Equation

The second quadratic equation is: \(x^2 - (b+c)x + bc = 0\)

This equation can be factored: We look for two numbers that multiply to \(bc\) and add to \(b+c\). These numbers are \(b\) and \(c\). So, the equation becomes: \((x - b)(x - c) = 0\)

The roots of this equation are \(x = b\) and \(x = c\).

Relating Roots to A and G

We found that \(A = b\) and \(G = c\). The roots of the second equation are \(b\) and \(c\). Therefore, the roots of the equation \(x^2 - (b+c)x + bc = 0\) are A and G.

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Similar Questions

  1. If the graph of a quadratic polynomial lies entirely above x-axis, then which one of the following is correct?

  2. If the roots of the equation x 2+ px + q = 0 are tan 19° and tan 26°, then which one of the following is correct?

  3. If x 2- px + 4 > 0 for all real values of x, then which one of the following is correct?

  4. How many real roots does the equation x 2+ 3|x| + 2 = 0 have?

  5. What is the GM of the roots of the equation ?

  6. In solving a problem that reduces to a quadratic equation, one student makes a mistake in the constant term and obtains 8 and 2 for roots. Another student makes a mistake only in the coefficient of first-degree term and finds -9 and -1 for roots.

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Important Questions from Quadratic Equations

  1. If the graph of a quadratic polynomial lies entirely above x-axis, then which one of the following is correct?

  2. If the roots of the equation x 2+ px + q = 0 are tan 19° and tan 26°, then which one of the following is correct?

  3. If x 2- px + 4 > 0 for all real values of x, then which one of the following is correct?

  4. If 2 + i is a root of the equation x 2- ax + 1 = 0, then the value of a is:

  5. If \(\tan \left( {\frac{α }{2}} \right)\)  and  \(\tan \left( {\frac{β }{2}} \right)\)  are the roots of the equation 8x 2- 26x + 15 = 0, then the value of cos (α + β) will be

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