Perpendicular lines meet at right angles
Angles in the straight line
It is not an axiom, but a theorem.
If two of the angles of a parallelogram are acute, then the other two angles will be obtuse. Since a parallelogram contains two pairs of parallel sides, both of the acute angles and both of the obtuse angles respectively will measure the same.
If they meet at right angles
If you mean a ratio of 7 to 9 then the other two angles are 35 degrees and 45 degrees respectively
Two straight lines that meet at right angles are perpendicular.
Perpendicular lines meet at right angles
Angles in the straight line
It is not an axiom, but a theorem.
If two of the angles of a parallelogram are acute, then the other two angles will be obtuse. Since a parallelogram contains two pairs of parallel sides, both of the acute angles and both of the obtuse angles respectively will measure the same.
The other two angles each measure 90 degrees
If they meet at right angles
Only if they meet.
The opposite angles are simply called opposite angles. They always have the same measure.
perpendicular
The combined size of the other two angles of a right triangle is 90 degrees.