If 3x + (3/x) = 5, then x3 + (1/x3) = ?
সমাধান
সঠিক উত্তর: Option C
দেয়া আছে,
3x + (3/x) = 5
বা, x + (1/x) = 5/3
∴ x3 + (1/x)3
= {x + (1/x)}3 - 3.x.(1/x){x + (1/x)}
= (5/3)3 - 3 × (5/3)
= (125/27) - 5
= (125 - 135)/27
= - (10/27)
3x + (3/x) = 5
বা, x + (1/x) = 5/3
∴ x3 + (1/x)3
= {x + (1/x)}3 - 3.x.(1/x){x + (1/x)}
= (5/3)3 - 3 × (5/3)
= (125/27) - 5
= (125 - 135)/27
= - (10/27)
