Question

what is $m\angle 1$?
triangle with angle 1 at top, 69° at bottom right, and an exterior angle of 123° at bottom left
$m\angle 1 = \square^\circ$
submit

Explanation:

Step1: Find adjacent interior angle

The 123° angle is supplementary to the triangle's interior angle next to it.
$180^\circ - 123^\circ = 57^\circ$

Step2: Sum of triangle angles is 180°

Subtract the two known interior angles from 180° to find $\angle1$.
$m\angle1 = 180^\circ - 57^\circ - 69^\circ$

Step3: Calculate final value

Compute the remaining angle measure.
$m\angle1 = 54^\circ$

Answer:

$54$