مقدار زاویه x چند درجه است؟
84 درجه
111 درجه
138 درجه
69 درجه
\(\begin{array}{l}2a + 2b + 42 = 180\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,a + b + x = 180\\ \Rightarrow 2a + 2b = 180 - 42 = 138\\ \Rightarrow 2\left( {a + b} \right) = 138\,\,\, \Rightarrow \,\,\,\left( {a + b} \right) = \frac{{138}}{2} = 69\\\\a + b + x = 180\,\,\, \Rightarrow \,\,\,x + 69 = 180\,\,\, \Rightarrow \,\,\,x = 180 - 69 = 111\end{array}\)