The roots of the equation 7x2 - 6x + 1 = 0 are tan α and tan β, where 2α and 2β are the angles of a triangle. Which one of the following is correct?

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NDA-II 2024 (Maths) Official Paper (Held On: 01 Sept, 2024)
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  1. The triangle is equilateral
  2. The triangle is isosceles but not right-angled
  3. The triangle is right-angled
  4. The triangle is right-angled isosceles

Answer (Detailed Solution Below)

Option 3 : The triangle is right-angled
Free
NDA 01/2025: English Subject Test
30 Qs. 120 Marks 30 Mins

Detailed Solution

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Explanation:

Given:

tanα and tanβ are roots of 7x2 – 6x + 1 = 0

Hence, 

⇒ tanα + tanβ = 6/7...(1)

⇒ tanα.tanβ = 1/7...(2)

⇒ tan(α+β) = 

⇒ α +β = 4

⇒ 2α +2β = 90°

It means the third angle of a triangle is 90°.

Hence, the triangle is right-angled.

Since

⇒tanα - tanβ = 

Also

⇒ tan(α -β) =  = 

⇒ tan2(α -β) = 

 = 

Thus 2α≠2β 

∴ Option (c) is correct.

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