## Algebra: A Combined Approach (4th Edition)

$17.4°$
Since the triangle is a right-angled triangle, the second angle is $90°$. Furthermore, the sum of the measures of the angles of a triangle is $180°$. Since one angle measures $72.6°$ and the other angle measures $90°$, the third angle measures $180°-72.6°-90°=17.4°$.