Use angle facts and diagram structure to find unknown angle measures.
Use shape angle totals
Problem
\(\text{Two}~\text{angles}\) in a triangle measure \(48°\) and \(77°\). What is the measure of the \(\text{third}~\text{angle}\)?
Big Picture
What this problem is really about
Use the figure’s invariant before working with the particular numbers: every triangle’s interior angles share the same total. Combine the two known measures first, then treat the third angle as the remaining part of that total. A final three-angle sum checks both the subtraction and the choice of geometric fact.
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