Create and solve one-variable equations and inequalities from contexts using all studied expression types, including simple root functions.
Determine which solutions to a modeled equation are valid in context
Problem
An elapsed-time model gives \(t~=~-2\) and \(t~=~5~\text{seconds}\) after a timer starts. Determine the context-valid solution.
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What this problem is really about
An equation can produce algebraic candidates that the story itself rules out. Translate “elapsed time after the timer starts” into a nonnegative domain, then test each candidate against that condition. Keep only values that satisfy both the equation and the meaning, units, and physical limits of the variable.
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