Stage: 5 Challenge Level: 
Prove that the sum
$$ \sum_{t=0}^m {(-1)^t\over t!(m-t)!} = 0 $$
Generalising. Creating expressions/formulae. Manipulating algebraic expressions/formulae. Patterned numbers. Mathematical reasoning & proof. Number theory. Visualising. Binomial Theorem. Dynamical systems. Inequality/inequalities.
Published January 2003.
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