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.

Answer 1

less than 90°.

Reason: In any triangle A + B + C = 180°. If B is obtuse (B > 90°) then A + C = 180° − B < 90°, so each of A and C must be less than 90°.