## Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

$\text{True}$
A right triangle has one angle whose measurement is $90°$. In all triangles, the sum of the three angles equals to $180°$, therefore if a triangle has one angle of $90°$, the sum of the two other must equal to $180°-90°=90°$. Hence, the given statement is true.