Question

For the triangle shown in the picture two angles are given find the third angle without using a protractor.

Answer 1

Let's use x for the missing angle. The sum of the internal angles of a triangle is equal to 180°. Then we have:

$\begin{gathered} 180^{\circ}=x+29^{\circ}+109^{\circ}=x+138^{\circ} \\ 180^{\circ}=x+138^{\circ} \end{gathered}$

Then if we substract 138° from both sides we get:

$\begin{gathered} 180^{\circ}-138^{\circ}^{}=x+138^{\circ}-138^{\circ} \\ x=42^{\circ} \end{gathered}$

Then the answer is 42°.