Question

find the measure of ∠x.
138° 31°
x
m∠x = □°

Explanation:

Step1: Find the non - labeled angle adjacent to 138°

The non - labeled angle adjacent to 138° and 138° are supplementary. So the measure of this angle is $180^{\circ}- 138^{\circ}=42^{\circ}$.

Step2: Use the angle - sum property of a triangle

In the triangle formed, the sum of the interior angles of a triangle is 180°. Let the third angle in the triangle be $x$. We know two angles of the triangle are 42° and 31°. So $x = 180^{\circ}-(42^{\circ}+31^{\circ})=107^{\circ}$.

Answer:

$107$