Problem 1
Use the precise definitions, state all hypotheses, apply |x+y|≤|x|+|y|, and verify the conclusion against a boundary case or independent theorem.
Faculty solution guide
Absolute Value, Intervals and the Triangle Inequality
Accept equivalent mathematically correct reasoning. Require explicit definitions, theorem hypotheses, proof structure, verification, and limitations.
Problem 2
Identify the first invalid inference, missing hypothesis, quantifier error, unjustified limit interchange, or unproved existence claim; then supply a valid repair.
Problem 3
A complete response explicitly states the definitions, domain, hypotheses, exact target, and theorem dependencies for Absolute Value, Intervals and the Triangle Inequality.
Problem 4
The argument must address proving inequalities and translating neighborhoods with each nontrivial step justified and the final conclusion restated.
Problem 5
A strong application explains the mathematical model in foundations of calculus, numerical bounds, optimization, and rigorous modelling, verifies conditions, and names at least one limitation.
Problem 6
Accept a second valid proof, a counterexample showing necessity of a hypothesis, an independent estimate, or a reproducible finite check that is correctly described as supporting evidence.