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: Define an obtuse angle

An obtuse angle is an angle greater than 90° and less than 180°. In triangle ABC, ∠B>90°.

Step3: Analyze the other angles

Let ∠A + ∠B+∠C = 180°. Since ∠B>90°, then ∠A + ∠C=180° - ∠B<90°. So, both ∠A and ∠C must be less than 90°.

Answer:

less than 90°.