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GMAT Quantitative Practice
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If x + y = 10 and xy = 21, what is the value of x^2 + y^2?
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A
69
💡 Explanation:
Using the identity (x + y)^2 = x^2 + y^2 + 2xy, we can solve for x^2 + y^2: (x + y)^2 = x^2 + y^2 + 2xy 10^2 = x^2 + y^2 + 2(21) 100 = x^2 + y^2 + 42 x^2 + y^2 = 100 - 42 = 58.