যদি  α এবং β , x2 – x – 1 = 0 এই সমীকরণের মূল হয় তবে α/β এবং β/α যে সমীকরণের মূল, সেই সমীকরণটি হবে :

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RRC Group D Previous Paper 2 (Held On: 18 Sep 2018 Shift 1)
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  1. x2 + 3x – 1 = 0
  2.  x2 + x – 1 = 0
  3.  x2 – x + 1 = 0
  4.  x2 + 3x + 1 = 0

Answer (Detailed Solution Below)

Option 4 :  x2 + 3x + 1 = 0
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Detailed Solution

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প্রদত্ত :

x2 – x – 1 = 0

অনুসৃত সূত্র :

যদি প্রদত্ত সমীকরণটি হয়  ax2 + bx + c = 0

মূলগুলির যোগফল = -b/a

এবং মূলগুলির গুণফল = c/a

গণনা :

 যদি α এবং β  x2 – x – 1 = 0 এর মূল হয়, তবে

⇒ α + β = -(-1) = 1

⇒ αβ = -1

এখন, যদি (α/β) এবং (β/α) মূল হয়, তবে,

⇒ মূলগুলির যোগফল = (α/β) + (β/α)

⇒ মূলগুলির  যোগফল = (α2 + β2)/αβ

⇒ মূলগুলির যোগফল= [(α + β)2 – 2αβ]/αβ

⇒ মূলগুলির  যোগফল = (1)2 – 2(-1)]/(-1) = -3

⇒ মূলগুলির গুণফল = (α/β) × (β/α) = 1

এখন, সমীকরণটি হল-

⇒ x2 – (মূলগুলির  যোগফল) x + মূলগুলির  গুণফল= 0

⇒ x2 – (-3)x + (1) = 0

⇒ x2 + 3x + 1 = 0 
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