If AM and GM of roots of a quadratic equation are 8 and 5 respectively. Find quadratic equation?

  1. x2 - 16x - 25 = 0
  2. x2 - 16x + 25 = 0
  3. x2 + 25x - 16 = 0
  4. x2 - 25x - 16 = 0

Answer (Detailed Solution Below)

Option 2 : x2 - 16x + 25 = 0
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NDA 01/2025: English Subject Test
30 Qs. 120 Marks 30 Mins

Detailed Solution

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Concept:

If A is the arithmetic mean of numbers a and b and is given by: 

If G is the geometric mean of the numbers a and b and is given by: 

Calculation:

Let α and β be the two roots of the quadratic equation

Given:

The arithmetic mean of the roots of a quadratic equation is 8

Therefore, 

⇒ α + β = 16

Now, geometric mean of the roots of a quadratic equation is 5.

Therefore, 

Squaring both sides, we get

⇒ αβ = 25     

Thus, the required equation is:

⇒ x2 - (Sum of the roots) x + product of the roots = 0

⇒ Thus, the required equation is:

⇒ x2 - (α + β) x + αβ = 0

⇒ x2 -16x + 25 = 0

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