Question

If x-y = 5
and xy=7
Find the value of - x cube minus y cube
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Answer 1

${x - y} = 5 \\ {x}^{3} - {y}^{3} - 3xy(x - y) = 125 \\ {x}^{3} - {y}^{3} - 3 \times 7 (5) = 125 \\ {x}^{3} - {y}^{3} - 105 = 125 \\ {x}^{3} - {y}^{3} = 125 + 105 \\ {x}^{3} - {y}^{3} = 230$