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    If 3x-2y=10 and xy=11, the value of 27x3−8y327x^3-8y^327x3−8y3​ is
    Question

    If 3x-2y=10 and xy=11, the value of 27x38y327x^3-8y^3​ is

    A.

    2980

    B.

    2569

    C.

    3336

    D.

    3170

    Correct option is A

    Given:
    3x - 2y = 10 and xy=11

    Formula used:
    (ab)3=a3b33ab(ab)(a - b)^3 = a^3 - b^3 - 3ab(a - b) \\​​
    Solution: 
    3x2y=10Taking a cube on both sides of the above equation:(3x2y)3=10327x38y33(3x)(2y)(3x2y)=100027x38y318(xy)(3x2y)=1000Substitute: 3x2y=10, xy=1127x38y3181110=100027x38y31980=100027x38y3=1980+100027x38y3=2980Hence, the value of 27x38y3 is 2980.3x - 2y = 10 \\\text{Taking a cube on both sides of the above equation:} \\(3x - 2y)^3 = 10^3 \\27x^3 - 8y^3 - 3(3x)(2y)(3x - 2y) = 1000 \\27x^3 - 8y^3 - 18(xy)(3x - 2y) = 1000 \\\text{Substitute: } 3x - 2y = 10, \, xy = 11 \\27x^3 - 8y^3 - 18 \cdot 11 \cdot 10 = 1000 \\27x^3 - 8y^3 - 1980 = 1000 \\27x^3 - 8y^3 = 1980 + 1000 \\27x^3 - 8y^3 = 2980 \\\textbf{Hence, the value of } 27x^3 - 8y^3 \text{ is } 2980.​​

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