Assuming the property is false and showing this leads to an impossibility. Contraposition: Proving "If not B, then not A."
∑i=1k+1fi2=(∑i=1kfi2)+fk+12sum from i equals 1 to k plus 1 of f sub i squared equals open paren sum from i equals 1 to k of f sub i squared close paren plus f sub k plus 1 end-sub squared Substitute the inductive hypothesis: stefani_problem_stefani_problem
Proving a base case and showing the property holds for if it holds for Assuming the property is false and showing this
In the De Stefani curriculum, problems are designed to test five fundamental proof techniques: stefani_problem_stefani_problem