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2025 AMC 12B Problem 3

Problem 3 of 25EasierAlgebra

What is the value of i(i−1)(i−2)(i−3),i(i-1)(i-2)(i-3), where i=−1?i = \sqrt{-1}?

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Solution

i(i−1)=i2−i=−1−i,i(i-1) = i^2 - i = -1 - i, and (i−2)(i−3)=i2−5i+6(i-2)(i-3) = i^2 - 5i + 6 =5−5i.= 5 - 5i. Then (−1−i)(5−5i)=−5+5i−5i+5i2=−5−5=−10. \begin{gathered} (-1-i)(5-5i) = -5 \\ {}+ 5i - 5i \\ {}+ 5i^2 \\ = -5 - 5 = -10. \end{gathered} Thus, the correct answer is D.
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