Yes
All three interior angles of a spherical triangle may be right angles.
8
That is an important theorem in geometry: if two lines intersect to form adjacent congruent angles, then the lines are perpendicular. Those congruent angles would be right angles.
Yes, although a triangle (in normal geometry) can only have one right angle, no more. It is possible for a triangle to have all three right angles in spherical geometry (if you were to draw the triangle on a sphere).
All right angles are congruent, and all straight angles are congruent.
A right trapezoid can have no congruent sides and two right angles.
Angles that are congruent and supplementary must be right angles.
right angles
There are four right angles in a square or rectangular geometry
A rhombus is a parallelogram with all four sides congruent to each other with no right angles. A square is a parallelogram with four congruent sides and four right angles.
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Vertical angles are always, by definition, congruent. Note: If the two vertical angles are right angles then they are both congruent and supplementary.