x2-3x+1=0 হলে (x2 - 1/x2) এর মান-

A 5√3

B 3√5

C 4√5

D 6√5

Solution

Correct Answer: Option B

x2-3x+1=0 
বা, x2-3x=-1 
বা, x(x-3)=-1 
বা, x-3=-1/x
বা, x+1/x=3 
বা, (x+1/x)2=32 
বা, (x+1/x)2=9 
বা, (x-1/x)2+4.x.1/x=9 
বা, (x-1/x)2=9-4 
বা, (x-1/x)2=5 
বা, x-1/x=√5 
এখন, x2-1/x2=(x+1/x) (x-1/x) =3√5

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