The diagram shows a right angle and an additional angle of $26^\circ$. The goal is to find the missing angle, $a$.

Since the angles form a right angle (90°) in total, we can calculate the missing angle by subtracting the given angle from 90°.

$a = 90^\circ - 26^\circ = 64^\circ$

Therefore, the measure of the missing angle $a$ is $64^\circ$.

Would you like further details or have any questions?

Here are some related questions you might find useful:

1. How do you find the measure of angles in different types of triangles?
2. What is the sum of angles in a triangle?
3. How can you use complementary and supplementary angles in solving problems?
4. How do you solve for an unknown angle in a polygon?
5. What are the properties of different types of angles (acute, obtuse, right)?

Tip: Always check if the angles form any special type (like complementary or supplementary) to simplify calculations.