The image shows a right-angle triangle with one of the angles marked as $40^\circ$. Since one angle is $90^\circ$ (the right angle) and the sum of the angles in any triangle is $180^\circ$, we can calculate the missing angle.

Step-by-step solution:

1. The sum of the angles in a triangle is $180^\circ$.
2. One angle is $90^\circ$ (the right angle), and another is $40^\circ$.
3. The missing angle can be calculated as: $\text{Missing angle} = 180^\circ - 90^\circ - 40^\circ = 50^\circ$

Thus, the missing angle is $50^\circ$.

Let me know if you'd like more details, or if you have any questions.

Here are 5 related questions:

1. What is the sum of the interior angles in any triangle?
2. How do you determine if a triangle is right-angled?
3. Can a triangle have two right angles? Why or why not?
4. How can you calculate the third angle of a triangle if two angles are known?
5. What types of triangles have a $90^\circ$ angle?

Tip: Always check that the sum of all angles in a triangle equals $180^\circ$, regardless of its type!