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If $x + y = 10$ and $x y = 21$ , then $x^{3} + y^{3}$ equals:

Competition practiceAlgebra

A1000
B730
C370
D580

Step-by-Step Solution

x^{3} + y^{3} = (x + y)^{3} - 3 x y (x + y) = 1000 - 3 \times 21 \times 10 = 1000 - 630 = 370

. (Indeed

x, y = 3

, 7 and 27 + 343 = 370.)

Answer: C) 370

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