The image shows a geometric problem involving a semicircle and triangles. Let's analyze the content and answer the questions.

Problem Analysis:

1. 問1: What type of triangle is △OAB?
2. 問2: What is the measure of the central angle labeled ⑦?

Solution:

1. 問1 (Type of △OAB):

   • The figure shows a semicircle with diameter $OB$. Triangle $OAB$ is inscribed in the semicircle with $OB$ as its hypotenuse.
   • By the Inscribed Angle Theorem, any triangle inscribed in a semicircle with the diameter as one side is a right triangle.
   • Therefore, △OAB is a right triangle with a right angle at point $A$.

2. 問2 (Measure of the central angle labeled ⑦):

   • Central angle ⑦ is subtended by arc $AB$ of the semicircle. In a semicircle, the central angle that subtends the entire diameter is always $180^\circ$. However, since this question specifically refers to angle ⑦, which likely subtends only a segment of the semicircle:
   • The measure of angle ⑦ depends on the specific configuration shown. Without precise measurements, it's challenging to provide an exact degree, but the information suggests it is proportional to the arc's length that angle ⑦ subtends.

Would you like more details on the central angle calculation, or do you have any other questions?

Related Questions:

1. How do you determine the type of a triangle inscribed in a semicircle?
2. What is the Inscribed Angle Theorem, and how does it apply to triangles in a semicircle?
3. How do you calculate central angles in circles when given arcs?
4. What properties do right triangles have when inscribed in semicircles?
5. Can the measure of angle ⑦ be determined exactly without additional data?

Tip: Always remember that a triangle with one side as the diameter of a semicircle is a right triangle, a key property of semicircle inscribed figures.