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1+a1111+b1111+c=abc+ab+ac+bc\left|\begin{array}{ccc} 1+a & 1 & 1 \\ 1 & 1+b & 1 \\ 1 & 1 & 1+c \end{array}\right|=a b c+a b+a c+b c

Solution

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Answered 1 year ago
Answered 1 year ago
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There are 99 lines rising to the right:

  • The line joining a51a_{51} and a32a_{32}
  • The line joining a51a_{51} and a43a_{43}
  • The line joining a51a_{51} and a24a_{24}
  • The line joining a51a_{51} and a15a_{15}
  • The line joining a32a_{32} and a24a_{24}
  • The line joining a32a_{32} and a15a_{15}
  • The line joining a43a_{43} and a24a_{24}
  • The line joining a43a_{43} and a15a_{15}
  • The line joining a24a_{24} and a15a_{15}

The sign is then ()(-) and the corresponding term of the determinant is equal to:

a51a32a43a24a15\begin{aligned} -a_{51}a_{32}a_{43}a_{24}a_{15} \end{aligned}

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