Question

Triangle ABC is an obtuse triangle with the obtuse angle at vertex B. Angle A must be

less than 90°.
greater than 90°.
congruent to angle B.
congruent to angle C.

Answers

GPT-4o mini
In triangle ABC, since angle B is the obtuse angle, it means that angle B is greater than 90°. In any triangle, the sum of all angles is equal to 180°. Since angle B is greater than 90°, the sum of angles A and C must be less than 90°.

This implies that:

- Angle A must be **less than 90°**.
- Angle C must also be **less than 90°**.

Therefore, the correct answer is that angle A must be **less than 90°**.