Triangle abc is an obtuse triangle with the obtuse angle at vertex b. angle a must be

a) less than 90°.
b) greater than 90°.
c) congruent to angle b.
d) congruent to angle c.

We have to find the correct statement for angle A in a triangle ABC, which is an obtuse triangle. We know that angle B is obtuse ( greater than 90 degrees ). Therefore angles A and C must be less than 90 degrees. Angle A can not be congruent to angle B ( angle B > angle A ). It can be congruent to angle C but just in case that ABC is an isosceles obtuse triangle. Angle A must be A ) less than 90 degrees.