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.

Explanation:

Step1: Recall triangle - angle sum property

The sum of the interior angles of a triangle is 180°.

Step2: Analyze the obtuse - angle case

Since angle B is obtuse (greater than 90°), and the sum of angles A + B + C=180°. So, angles A and C must be acute (less than 90°) to satisfy the angle - sum property of a triangle.

Answer:

less than 90°.