Advanced Math practice question

Answer: 126

x³ + y³ = (x + y)³ − 3xy(x + y) = 216 − 3(5)(6) = 216 − 90 = 126. (The numbers are 1 and 5: 1 + 125 = 126.)

Common wrong answers

If you answered 36

36 is (x + y)².

If you answered 186

186 subtracts 3xy = 15 twice instead of 3xy(x + y) = 90.

If you answered 216

216 is (x + y)³, forgetting to subtract 3xy(x + y).

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