Exercise 1 Page 304

Since $\angle 1$ is a right angle, we know $m\angle 1=90.$ Now, let's add some labels to the given diagram.

We can see that $\angle 1$ and $\angle ABD$ form a linear pair. Therefore, the Supplement Theorem gives us the following relation. We can find $m\angle ABD$ by substituting $m\angle 1=90$ into this equation. Now, since $\angle 2$ and $\angle 3$ are adjacent angles that form the right angle $\angle ABD,$ by using the Complement Theorem, we can say that $\angle 2$ and $\angle 3$ are complementary angles. To find the measure of $m\angle 3,$ we substitute $m\angle 2=26$ into the equation above and solve it. Finally, we found the measure of each numbered angle.