[Solved] If 2x + 3y = 14 and xy = 8, then the value of 8x3 + 27y |
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Given: 2x + 3y = 14 and xy = 8 Concept used: (a + b)2 = a2 + b2 + 2ab a3 + b3 = (a + b)(a2 - ab + b2) Calculation: 2x + 3y = 14 on squaring both side we get (2x + 3y)2 = 142 ⇒ 4x2 + 9y2 + 12xy = 196 ⇒ 4x2 + 9y2 + 12 × 8 = 196 ⇒ 4x2 + 9y2 = 100 now, 8x3 + 27y3 = (2x)3 + (3y)3 ⇒ (2x)3 + (3y)3 = (2x + 3y)(4x2 - 6xy + 9y2) ⇒ (2x)3 + (3y)3 = 14 × (100 - 6 × 8) ⇒ 14 × 52 = 728 ∴ The answer is 728. Alternate Method a3 + b3 = (a + b)3 - 3ab(a + b 8x3 + 27y3 = (2x + 3y)3 - 3 × 2x × 3y(2x + 3y) ⇒ 143 - 18 × 8 × 14 ⇒ 2744 - 2016 ⇒ 728 ∴ The answer is 728. Download Solution PDF Share on Whatsapp |
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