If x+y=12 and xy=27find xcube+ ycube
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x+y=12
Cubing on both sides
(x+y)³=(12)³
x³+y³+3xy(x+y) = 1728
x³+y³+3×27(12) = 1728
x³+y³+81(12) = 1728
x³+y³+972 = 1728
x³+y³ = 1728-972
x³+y³ = 756
Cubing on both sides
(x+y)³=(12)³
x³+y³+3xy(x+y) = 1728
x³+y³+3×27(12) = 1728
x³+y³+81(12) = 1728
x³+y³+972 = 1728
x³+y³ = 1728-972
x³+y³ = 756
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