Question

If a triangle is obtuse, then all angles do not measure less than 90°.

Which of these is logically equivalent to it?
Answer
If a triangle is not obtuse, then all angles measure less than 90°.
If a triangle is obtuse, then it has no angle measuring more than 90°.
If all angles of a triangle measure less than 90°, then the triangle is not obtuse.
If all angles of a triangle do not measure less than 90°, then the triangle is obtuse.