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Answer» If ( x - 1/x ) = 3+2√2 , Find the VALUE of 1/4(x³ - 1/x³)
We know, ★ ( a-b)² = a² + b² - 2ab So, ★ ( x - 1/x )² = x² + 1/x² - 2.x.1/x ➥ (x - 1/x)² = x² + 1/x² - 2 Now, keep value by equ(1) ➥ (3+2√2)² = x²+1/x² - 2 ➥3²+(2√2)²+2.3.2√2 = x²+1/x² - 2 ➥ x² + 1/x² = (9+8+12√2)-2 ➥ x² + 1/x² = 15 + 12√2 Again, ★(a³-b³) = (a-b)(a²+b²+ab) So, ➥ (x³ - 1/x³ ) = (x - 1/x)(x² + 1/x² + x . 1/x) ➥(x³ - 1/x³ ) = (x - 1/x)(x² + 1/x² + 1) keep value by equ(1) and (2) ➥ (x³ - 1/x³ ) = ( 3+2√2)(15+12√2+1) ➥ (x³ - 1/x³ ) = (3+2√2)(16+12√2) ➥ (x³ - 1/x³ ) = 4(3+2√2)(4+3√2) ➥ (x³ - 1/x³ ) = 4(12+9√2+8√2+12) ➥ (x³ - 1/x³ ) = 4(24+17√2) Now, calculate , ➥ 1/4 (x³ - 1/x³ ) = 4(24+17√2)/4 ➥ 1/4 (x³ - 1/x³ ) = (24 + 17√2) (Ans.) _____________________ |
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